Rolling Dice Before A Character's Action Reviews RPG & Card Board
Depends on the circumstances. If rolling for an attack, then generally speaking yes, as you could direct a moderate roll towards an easily hit target and criticals towards the really tough guy.
In some cases though, a roll can determine what a character is able to do, or change the circumstances for later actions. For instance if a character hits and kills a target, they may wish to move, if they don't, they're more likely to stay put. Another example is saving against an effect that impacts the abilities of a character.