user31772: Recently I was playing a game on chess.com (300 rating) and after the game the engine showed that this move was a mistake, losing two points of material.
[FEN ""]

1. e4 a5 2. d4 h5 3. f3 f6 4. c3 c6 5. Nh3 b6 6. Bc4 e6 7. O-O d6 8. Na3 b5 9.
Nxb5 Ba6 10. Qb3 cxb5 11. Bxb5+ Nd7 12. Bxa6 Rxa6 13. Nf4 Rb6 14. Qc2 g5 15.
Nxe6 Qe7 16. Nxf8 Kxf8 17. b3 Rc6 18. Ba3 Nb6 19. Rfd1

Is there a reason I should play f4 instead? It seems like a dangerous move that has no merit.

user70: 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.

user9025: You're not actually losing two points of material by playing Rfd1, but rather you're not gaining the advantage.
You currently have 3 pawns for a knight, which is roughly even, however black is somewhat cramped for space, their knight is undeveloped, their king is under x-ray attack from both the bishop on a3 and rook on f1, and they have two isolated pawns.
By pushing e5 or f4, you are threatening to open direct lines to the black king, eventually turning your positional advantage into a material advantage.
One possible continuation is:
[FEN ""]
[StartPly "36"]

1. e4 a5 2. d4 h5 3. f3 f6 4. c3 c6 5. Nh3 b6 6. Bc4 e6 7. O-O d6
8. Na3 b5 9. Nxb5 Ba6 10. Qb3 cxb5 11. Bxb5+ Nd7 12. Bxa6 Rxa6
13. Nf4 Rb6 14. Qc2 g5 15. Nxe6 Qe7 16. Nxf8 Kxf8 17. b3 Rc6 18. Ba3 Nb6
19. e5 Qd7 20. c4 Nd5 21. Qd2 Nb4 22. f4 g4 23. d5 Rc8 24. Rae1 h4 25.
Bb2 h3 26. g3 Qf5 27. Bc3 Rh7 28. a3 Na6 29. Bxa5 *

White has picked up another pawn, and now has two outside passed pawns. Black will have to give up more material to stop them and still has to contend with the pressure from the e5 pawn.

31772: <p>Recently I was playing a game on chess.com (300 rating) and after the game the engine showed that this move was a mistake, losing two points of material.</p>
<pre><code>[FEN &quot;&quot;]

1. e4 a5 2. d4 h5 3. f3 f6 4. c3 c6 5. Nh3 b6 6. Bc4 e6 7. O-O d6 8. Na3 b5 9.
Nxb5 Ba6 10. Qb3 cxb5 11. Bxb5+ Nd7 12. Bxa6 Rxa6 13. Nf4 Rb6 14. Qc2 g5 15.
Nxe6 Qe7 16. Nxf8 Kxf8 17. b3 Rc6 18. Ba3 Nb6 19. Rfd1
</code></pre>
<p>Is there a reason I should play f4 instead? It seems like a dangerous move that has no merit.</p>
 70: <p>In addition to what Herb said,</p>
<ol>
<li>your rook on <code>f1</code> is already perfectly placed; it lines up on the black king.</li>
<li>Further, <code>Rfd1</code> doesn't force any action. Thus Black has time to solidify his kingside. Indeed, in Stockfish's analysis, White returns that rook to <code>f1</code> two moves later.</li>
</ol>
<p>And you are correct, <code>f4</code> is a move that requires careful consideration. Good on you. However, it is hard to see how Black can exploit that open diagonal (<code>a7-g1</code>), having no black-squared bishop and a precariously placed queen.</p>
<p>Regarding <code>f4</code>, Stockfish rates the position at about +4:</p>
<pre><code>

    [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

</code></pre>
<p>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.</p>
<p>On <code>Rfd1</code>, Stockfish drops the score to +1.72:</p>
<pre><code>
    [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
</code></pre>
<p>Comparing the variations, you can see how the 2nd variation is much less dynamic and Black is in less danger.</p>
 9025: <p>You're not actually losing two points of material by playing Rfd1, but rather you're not gaining the advantage.</p>
<p>You currently have 3 pawns for a knight, which is roughly even, however black is somewhat cramped for space, their knight is undeveloped, their king is under x-ray attack from both the bishop on a3 and rook on f1, and they have two isolated pawns.</p>
<p>By pushing e5 or f4, you are threatening to open direct lines to the black king, eventually turning your positional advantage into a material advantage.</p>
<p>One possible continuation is:</p>
<pre><code>[FEN &quot;&quot;]
[StartPly &quot;36&quot;]

1. e4 a5 2. d4 h5 3. f3 f6 4. c3 c6 5. Nh3 b6 6. Bc4 e6 7. O-O d6
8. Na3 b5 9. Nxb5 Ba6 10. Qb3 cxb5 11. Bxb5+ Nd7 12. Bxa6 Rxa6
13. Nf4 Rb6 14. Qc2 g5 15. Nxe6 Qe7 16. Nxf8 Kxf8 17. b3 Rc6 18. Ba3 Nb6
19. e5 Qd7 20. c4 Nd5 21. Qd2 Nb4 22. f4 g4 23. d5 Rc8 24. Rae1 h4 25.
Bb2 h3 26. g3 Qf5 27. Bc3 Rh7 28. a3 Na6 29. Bxa5 *
</code></pre>
<p>White has picked up another pawn, and now has two outside passed pawns. Black will have to give up more material to stop them and still has to contend with the pressure from the e5 pawn.</p>
