any time wasted on side-characters is pointless and super aggravating. either give them full scope or cut them altogether.
I wouldn't go that far. To me there's kind of a spectrum for side characters ranging from a bit less important than your core characters down to throw away characters you only meet once. The throw away characters I would agree don't add much value, but I think there's still plenty of room for minor characters to play an interesting role.
To me I think it makes sense to have the majority of your content focused on the central characters and then have progressively less content for characters that are less connected with your core characters.
A big part of it depends on whether MC is allowed to have more than 1 love interest or if he is forced to choose 1 and be blocked off from the others when he does so. If he can only have 1 then side characters are pretty pointless. If he can be a player then minor characters are a good way to allow you to pace the game so that major characters require significant development while some of the minor characters are easy fucks.
A stripper would be an example of a good minor character that is easily fuckable without needing much of a story justification for it. The party girl friend of the "nice girl" would be another good option like that. The nice girl might be your real goal but if her slutty friend is ready to jump you right away, why not? There might be negative consequences so whether you take her up on it might depend on whether it's the type of game where "mistakes" are fixable.