Majority of the cases of using multiple accounts is using them for plunder purposes. It's a clear concensus between mods that they have said it's bannable.

However, there are cases some mods have said it's okay in certains situations. For example, before cross server sage, there needs to be a certain amount of people signed up or sage would not work for the day. Using many accs just to sign up so sage works not only benefits you but everyone else who is signing up in a low populated sever. This also can be applied to the activity rate requirement for gnw if there's like two guilds in a server. This seems like a solution for those asking for merges since merge don't happen frequently.