So f3 db2 is what leads to your combo right. That's the ideal situation but it's unsafe, meaning if you just do that expecting it to hit and they block you get punished for it. Now f34 only does 18% on hit so you'd rather hit your combo rather than just doing f34 every time, however it is safe (0 on block) so on block it's way better to do f34. The option select takes away your guess, so you can put in the same command and get the best case scenario whether they block it or if it hits them (if they block you get your safe string, if it hits you get your combo opportunity).