I've come across 1. e3 from one of my regular opponents quite often. These are my observations for why White might like this line:
- Psychological: White plays a non-theoretical, flexible opening that White is likely to have played far more than Black.
- Familiarity with an opening uses clock time more efficiently. Black may have to spend more time on the opening moves to check that there are no tactical deficiencies
- As you rightly state, the move liberates the Queen & Bishop
- Transpo tricks: White has the opportunity to transpo to English, reversed French, reversed Dutch & Queen pawn openings, e.g. the Colle
- Solidity: White has a solid structure which facilitates safe development & early castling
The Van't Krujis leads to many opening lines, the named ones from Wikipedia are:
Keoni-Hiva Gambit: 1.e3 d5 2.Nc3 Nf6 3.a3 e5 4.f4 exf4 5.Nf3
- White gambits he pawn to castle kingside & target f7
- White often plays b5 to either fianchetto the queen side bishop to attack the king side
- Black sometimes jettisons the d5 pawn to the c3 knight with Nxd5 to reduce White's initiative
- Also, 3. a3 prevents a disruptive Bb4, threatening to remove the knight & simplifying when Black will soon be up a pawn
Amsterdam Attack: 1.e3 e5 2.c4 d6 3.Nc3 Nc6 4.b3 Nf6
- This is a transposition to the English opening, Bremen line
Ekolu Variation: 1.e3 e5 2.Nc3 d5 3.f4 exf4 4.Nf3
- Similar analysis to the Keoni-Hiva Gambit
Alua Variation: 1.e3 e5 2.Nc3 Nc6 3.f4 exf4 4.Nf3
- Similar analysis to the Keoni-Hiva Gambit
Akahi Variation: 1.e3 e5 2.Nc3 Nf6 3.f4 exf4 4.Nf3
- Similar analysis to the Keoni-Hiva Gambit
Bouncing Bishop Variation: 1.e3 e5 2.Bc4 d5 3.Bb3
- White aims to pressure the centre & Black's kingside with the Bishop on b3, similar to lines of the Ruy Lopez where White plays Bf1-b5-a4-b3