Why did F5 give white a +5 advantage?

Yavan

I feel that may be much… I can't really see a tactical finish… then again, I'm not a computer. They are quite amazing nowadays. But… white's development and pawn structure are superior, accounting for some of his advantage. (with or without f5?) After 12. ef (which also loses a pawn), the problems with it is it weakens the kingside, forces the loss of a tempi when Black is already late in development and Black's game is now very difficult, as he has very little mobility. (The f8 bishop is trapped, the g6 bishop has little prospect and the e7 knight is dominated. White has very strong control over the white squares, which Black desperately needs to complete his development.).