That depends. If I'm Nuzlocking, absolutely everyone gets a nickname, per the rules. If I'm not, however, I have a system for this. Everyone starts off without a nickname so I can kinda "test out" my catches. If I like them/they seem like solid choices for my team, I'll give them a nickname. If not, they just kinda get boxed. I know it sounds horrible, but I tend to stick with a core team, which not only consists of the main six but also tons of standbys. Nicknames help me to quickly identify who's on that team and who isn't. That and oftentimes, the unnicknamed ones are actually Wonder Trade fodder since Wonder Trade is my jam.