During character generation for my current Savage Worlds Necessary Evil Super-Hero campaign I let the players make anything they wanted without thought for campaign balance. When it comes to character generation some GMs disallow certain classes, races, and abilities as they would be too disruptive to the planned campaign. Such things as playing an elf when the elves of the world are all going to be the enemy or a mental ability that can probe the mind in a campaign full of secrets. In a game with super-powers disruptive abilities are especially prevalent. But I let them choose whatever they wanted.
With one caveat. Whatever powers they chose I would allow my NPCs antagonists to also have. If they took the ability that drains the life from an opponent killing the target with a single attack (Infection-Strong), I would have an NPC that could do that as well. So, while I did not "disallow" certain powers and power combos, they decided to avoid the more broken powers/combos. In effect, they chose powers that they were willing to face.
This became even more apparent during last night's game when one of the players was talking about how he would like to make another character that could be Invisible, have Extra Attacks, Teleport 3 times, using Paralyze on 3 opponents per round of action. Something like this is possible within the rules. But then the player next to him remarked that this is not something they would want to face in an opponent so it is best never done as a player character.
I love it when the players regulate themselves.