Is there any benefit to mega evolving multiple of the same pokemon?

Question in the title, but is there any benefit to it if let's say you have a hundo Garchomp and a 15/15/14 Garchomp, is there any point in mega evolving both of them or just the one with the high IVs? You can't use more than one mega pokemon at once anyway.

Once you've mega evolved a pokemon once it's easy to get more mega energy, so if you find one with better IVs later on you can get it mega evolved and use it.