I wasn't talking about waiting to see the proc first, but if you have a passive bash and "prime" it by hitting a creep and it doesn't proc, then the subsequent attack would apparently have a higher chance of hitting due to this mechanic, and not the actual % given. You could prime a crit or a bash before fighting a hero, first hit bash can make a big difference. But as stated by someone else this in practice is not easy to incorporate into a game and you are probably just as often wasting time.
