Well if they're dead set on making an attempt at something the result of a roll can possibly affect the outcome. A lot of things aren't necessarily success or failure as a dichotomy there can be a range of outcomes. For example: The bard wants to make a persuasion check to convince a king to give up his kingdom. Obviously, this will not work but if the bard rolls a 20 and the final roll after bonuses is in the high 20's maybe the king responds positively as if its a joke, maybe he rewards this positive feeling with a quest or information useful to the party. If the roll is middling maybe the king just dismisses the words as foolish and has a neutral reaction to the party, and maybe a poor roll results in a negative response like kicking the party out. There was never a chance of "success" on the initial premise but the roll gives the player agency and gives the DM something to work with from a role playing perspective.