Have an edge over yourself
It's not funny to gamble tbh, some people do it for fun but where's smartness in losing your money? Will you be called smart? No, right? It's better to only use and invest your bankroll in those games over which you have an edge. If you are sure about the game you are betting, then only use your 1 unit on that game, otherwise no need to gamble based on half (or 0) knowledge because we are talking about smart gambling and managing our bankroll. This assures that you have higher chances of winning over losing, and this edge will only help you gaining much more profits in the long run. If you don't know about a game, or yours is a few days ahead, just don't gamble and wait some days and let your expected game arrive.
This is key.
If you don't have an edge or a perceived positive expected value then there is really no point in managing your bankroll. You're going to be hit with the same negative long run EV in the long run.
The reason for bankroll management is to minimise your
risk of ruin and thereby dodging the variance that comes with a game of chance where you know you have an edge. And this is not only limited to sportsbetting - it applies to any AP across poker, BJ, etc.
If you are purely playing for fun then I don't see the point of rigidly managing your bankroll, just go out there and yolo.