Each Cold storage holds fifteen heroes ( 3x 5 hero team ).
Heroes in storage can not be leveled, or used, but do not count for roster space. Heroes in storage do not show up on the hero roster. like Niantic’s Key lockers hold keys that cannot be used but do not show up in inventory or count against inventory. ( Edit: this might not work for Empires. Maybe a slider "Show storage heroes " / "Hide storage heroes " for hero roster pages ).
Cold Storage has a rarity. Rare can hold 3* or lower. Epic can hold 4* or lower. Legendary can hold 5* or lower.
Each rarity has a maximum of five cold storage.
If you bought all five Rare cold storage, you could hold 75x 3* heroes in storage.
Each rarity is more expensive than the lower rarity.
Fifth Epic Cold Storage might cost X gems while First Legendary Cold Storage might cost 3* X gems.
Each additional cold storage increases rapidly.
First Epic Cold Storage might cost Y gems, but second costs 3* Y gems.
Removing heroes from the level up screen, class quest selection screen, war selection screen.
future trade heroes ( looking at you Wu Kong )
duplicates ( looking at you Anzogh)
Organizing future teams to level ( looking at you rainbow 5* 2.60 team)
Storing fully leveled 3*, or lower, heroes.