I have not played this opening ever, and I am not qualified to answer it, I have not found many creditable sources for my answer, but I did manage to find a few.
The Scheveningen Variation is a classically motivated defense. Black creates a backward pawn center with his duo at d6 and e6, leaving no weakness on the important central squares d5 and e5. Black intends to simply develop his pieces and then proceed with queenside counterplay. The Scheveningen has been a favorite of Kasparov's, although he often arrives at the position through transposition, playing 5…a6 and 6…e6.
Other top players use the defense frequently and it is well respected, but it doesn't have the devoted following of the Najdorf or Dragon Variations, perhaps because it is too straightforward and logical. White has several ways to combat the Scheveningen Variation, almost all of them leading to dynamic positions.
The Scheveningen Variation, named for a town in Holland, combines …e6 with …d6, instead of the …Nc6…d6 combination of the Classical. The pawn at e6 can serve as a target for White’s tactical operations. Sacrifices of a knight or bishop on that square are almost routine. The most exciting lines start with 6.Bc4 and are known as the Sozin Variation. Opposite wing castling can lead to very double-edged games.
The Scheveningen features the "small center" for Black, with the pawns at d6 and e6 keeping the enemy pieces at bay. For the most part, Black pawns will remain behind the front lines, mostly on the third rank. White will not have very many weaknesses to work against, and precision is required by both sides. For this reason the top player in the world are frequently seen on both sides of the opening.
The much-feared Keres Attack is the greatest disincentive by white to Black's move order. The Keres Attack is the sharpest response to the Scheveningen, favored by attacking players. However it is by no means clear that White has a guaranteed advantage, but the results overwhelmingly favor White. So even Kasparov, who loved to defend the Scheveningen, often arrived via a Najdorf route to avoid the Keres Attack.
Scheveningen Variation, Keres Attack (with ...h7-h6)(Favors White)
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g4 White immediately starts his Kingside attack in motion. The threat to play g4-g5 and kick the f6-Knight into oblivion is one that theorists have long debated. Sould Black allow White to carry out his threat, or play ....h7-h6, creating a weakness? This queston produces two distinct variations. Keres Attack (without ....h7-h6) and Keres Attack (with ....h7-h6) the one we will now look at. Scheveningen players by and large prefer to slow down White's expansion by playing
6...h6 7.g5 hxg5 8.Bxg5 At this point is extreamely difficult to evaluate this position. Black's h8-Rook has been "developed" with having moved, a certain plus for Black. The trade of a Black h-pawn for a White g-pawn means that neither player is going to castle on the Kingside. Probably both Kings will move Queenside. White's menacing g5-Bishop must be carefully observed as the tactics of f2-f4 and e4-e5 will hang over Black's position. A usual continuation would be;
8...Nc6 9.f4 Be7 10.Qd2 a6 11.0-0-0 Qc7 12.h4 Bd7 This leads to another one of those bottomless Sicilian positions that defy conventional understanding. Theorists have a slight preference for White in this position.
Scheveningen Variation, Keres Attack (without ...h7-h6) (Favors White)
Black can allow White to carry out his threat, as follows
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g4 Nc6 7.g5 Nd7 8.Be3 a6 9.h4 Qc7 10.f4 b5
White has extended his Kingside in order to launch an attack, while Black is busily preparing ...Bc8-b7 and ...Nd7-c5 with a counterattack against the e4-pawn. This position is uncommonly sharp. White has a slight advantage.
Scheveningen Variation, Fischer Attack (Equal Position)
The Fischer Attack is a straight-forward concept that begins
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.Bc4 White tries to clamp down on the d5-square, with an eye toward attacking the e6-pawn with f2-f4-f5. Black has a variety of defenses based upon ...Nb8-c6=a5 or ...Nb8-s7-c5 in conjunction with ...a7-a6 and ...b7-b5-b4 going for the e4-pawn. A solid choice is:
6...Be7 7.Bb3 0-0 8.Be3 White prepares to castle Queenside.
8...Na6 Black decides to bring his Knight to the c5-square to eliminate the b3-Bishop. One of the tactics that Black has to be aware of is; [8...Nbd7 9.Bxe6!? fxe6 10.Nxe6 Qa5 11.Nxf8 Bxf8 White sacrifices two pieces for a Rook.]
9.Qe2 Nc5 10.f3
This is a common position from the Fischer Attack. White will aim for g2-g4-g5 and a big Kingside pawn storm. Black will play ...a7-a6 and ...b7-b5 for an attack on the Queenside. This position is dynamically ballanced.
Scheveningen Variation, Maroczy Variation (Equal Position)
In the Maroczy Variation, White takes a more restrained approach to the center. He, she, it aims to complete his kingside development, delaying an attack for awhile.
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.Be2 Be7 7.0-0 Nc6 8.Kh1 White tucks his King away to the h1-square. He is committed to playing f2-f4, and wants to avoid tactics based on the g1-a7 diagonal
8...0-0 9.f4 a6 Black guards the b5-square and prepares the c7-square for his Queen.
In their 1995 PCA Championship Match, Viswanathan Anand and Garry Kasparov played this position a number of times. The position is dynamically balanced.
Scheveningen Variation, Tal Variation (Equal Position)
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6
The Tal variation has a completely different plan by White. Mikhail Tal (1936-1992), World Champion, 1960 to 61, was a master of the attack, and introduced the scheme of a quick Queenside castling;
6.f4 White wants to create immediate central threats with e4-e5. Black has to keep a wary, cautious, careful, eye to guarding against this possibility of danger to this possibility.
6...Nc6 7.Be3 Be7 8.Qf3
This position shows Tal's idea. What he wants to do is quickly castle Queenside and reintroduce the threat of e4-e5 after White's Rook is sitting on the d1-square. In many lines, when the players castle on opposite wing, Whit's Queen is ready to support the charge of the g-pawn. The position is dynamically balanced.
There are other plans. White can continue with simple development or go for broke on the kingside with the dangerous Keres Attack, which begins 2…d6; 3d4 cxd4; 4.Nxd4 Nf6; 5.Nc3 g6; 6.g4. Often Black plays this Sicilian defensively, trying to create impregnable barriers. A Hedgehog Position is often the result.