In addition to what Herb said,
- your rook on
f1
is already perfectly placed; it lines up on the black king.
- Further,
Rfd1
doesn't force any action. Thus Black has time to solidify his kingside. Indeed, in Stockfish's analysis, White returns that rook to f1
two moves later.
And you are correct, f4
is a move that requires careful consideration. Good on you. However, it is hard to see how Black can exploit that open diagonal (a7-g1
), having no black-squared bishop and a precariously placed queen.
Regarding f4
, Stockfish rates the position at about +4:
[FEN "5knr/4q3/1nrp1p2/p5pp/3PP3/BPP2P2/P1Q3PP/R4RK1 w - - 0 20"]
1.f4 gxf4 2.e5 Kg7 3.Rae1 Qd7 4.Bxd6 Rxd6 5.exd6 Qxd6 6.Qf2 Ne7 7.c4 Nbc8 8.Qxf4 Qxf4 9.Rxf4 Kf7 10.Ref1 f5 11.d5 Rh6 12.Rd4 Rd6 13.Re4 Kf6 14.Re2 Rd7 15.Re6+ Kg5 16.Ra6 Nxd5 17.cxd5 Rxd5 18.a3 Nd6 19.Ra8 Ne4 20.Rh8 Kg6
You can see by about the 6th move how ugly Black's position is getting. He's giving up material to take the pressure off.
On Rfd1
, Stockfish drops the score to +1.72:
[FEN "5knr/4q3/1nrp1p2/p5pp/3PP3/BPP2P2/P1Q3PP/R4RK1 w - - 0 20"]
1. Rfd1 Kf7 2.Rf1 Qb7 3.f4 gxf4 4.Rxf4 Nd7 5.c4 Ne7 6.Raf1 Ra6 7.R4f2 Ke8 8.Qd2 Qc7 9.Qe2 Qa7 10.Bb2 Kd8 11.Kh1 Nc6 12.Rd1 Kc8 13.Bc3 Kb8 14.Rf5 Kc8 15.Rb5 Qc7 16.a3 Rb6 17.d5 Rxb5 18.cxb5 Nb4 19.Bb2
Comparing the variations, you can see how the 2nd variation is much less dynamic and Black is in less danger.