We've put a lot of work into our clients and our backend to make sure the impact of being on 1 vs 100 guilds is negligible. It helps that most of the folks building Discord are power users in a bunch of servers (so we feel the pain of poorly optimized paths early). Generally if you don't look at a server often it shouldn't effect the performance of the app / bandwidth usage. I think we have some more blog posts in the works regarding some of these topics so look forward to those!