every site I take over has the same thing going on.
someone needed a contact form, installed a plugin.
needed to redirect one url, plugin.
wanted the excerpt a bit shorter, another plugin.
by the time it lands on my desk theres like 34 active and the homepage takes 6 seconds to load.

And half of them do stuff you could do in a few lines in functions.php or with the theme you already have. Some of them are fixing a problem the site doesn't even have anymore, it was relevant 3 years ago and just never got removed.

Speed is the obvious one but its not even the main thing imo.
Every plugin is one more thing that can break on an update, fight with another plugin, or just sit there unmaintained for ages being a quiet security hole. thats the part people don't think about.

what i tell people now is just ask if a visitor would actually notice it.
caching, fine.
security, fine.
some plugin that adds an animation to a button nobody clicks, probably not worth it.

I'm not saying run a bare install or rebuild everything yourself, thats dumb too. some plugins are doing real work and you'd be mad to recreate them. its more the leftover junk, the stuff you installed once to test something and forgot.

Anyway curious how other people handle it. do you keep to a rough number or just go case by case?