New player here, other than for fusions what is the purpose of keeping 2 or more copies of a champion? Especially 6-star ascended rare or higher grade champions like I see in some streams.
Unless they have a use, i.e. champions like Cold Heart, you could run teams of 4/5 of them and nuke high level dungeons etc. then there isn't.
As a new player, you will soon learn that 99% of rares (with the exception of Cold heart and Apoc) will be food, 90% of epics will be food and 50% oflegendaries.