We just released the first integration of a new feature we call "xp reserve".
Allow you to stack xp when you play using fully maxed characters. You can then use that xp in "My Collection" (we'll add this function to the collection pro as well) to level up your evolving characters.
How it works:
Your xp reserve has a max capacity based on your current level using that formula: max xp = 500 + your level * 100.
Then the extra xp is added automatically to your reserve at the end of each battle when you play using maxed characters (similar as how xp is added directly to the evolving characters).
We are going to add various ways to get capacity increases and maybe ways to get more xp in the reserve directly
It's still an early implementation but we couldn't wait!
There's still a point to training rooms.
Lots of 5* cards start off at level 2. That means 1500XP (2 -> 3*) + 3000XP (3* -> 4*) + 5000XP (4* -> 5*) = 9300 XP to fully evolve them. That's a lot of XP. So much, in fact, that you've got to be at least level 88 to fully evolve most 5* cards fresh from packs. Level 93 (500XP from 1* -> 2*) for a card like Kolos that starts at 1*.
It looks like it will be mostly useful as a "top off" to get a card into your deck more quickly, or to assure that a semi-evo card starts with a perfect 0XP at the desired level instead of 40, 95, 115, etc. Shaving off that spillover XP from lost warehouse will make them last an extra game or two in ELO.