Why two or three knots matter in a gun battle

Do two or three knots really matter in a visual-range naval gunfight?

Yes; speed may not change shell performance, but it controls whether and when the engagement occurs.

Naval battles do not begin with both sides already running parallel at ideal range. The faster force can choose whether to close from the moment ships first sight one another. It can also delay or refuse action when the tactical situation is unfavorable. Two or three knots matter because they help decide whether an engagement happens and who sets its opening geometry.