the difference is thay after 6.f3 the knight is loose and so black can try the annoying 6...Qb6. I'm not an expert on this line and I wonder whether white may try to sac the b pawn with 6.Be3!? anyway, looks like it should give some compensation. Good or not, it looks like 6.f3 just gives black an extra option and doesn't gain anything for white, therefore I would say 6.Be3! is more accurate.
White's move order in the Dragon/Yugoslav Attack
Thanks, I hadn't considered 6...Qb6 for some reason. I'm not sure it gives sufficient compensation, but there's only one game in the database with 6...Qb6 7.Be3 (the above one).
I had started playing 6.f3 to prevent 6...Ng4, but now I am thinking that is such a bad sixth move for Black that I shouldn't even care whether he plays it or not; in fact, I should hope that he does. It seems to straight-up win the exchange for White, actually - for example:
Is there any difference between 6. Be3 Bg7 7. f3 and 6. f3 Bg7 7. Be3?
Well obviously not, as what I typed is just a transposition, but what I'm wondering is if Black can take advantage of White somehow if White pushes f3 before getting the DSB out: