RiotWrekz's explanation on the changes to Muramana on the PBE.

https://www.reddit.com/r/leagueoflegends/comments/463yf2/216_pbe_update/d02dv2e

Agree that it makes the game easier. Thouh there was a certain satisfaction to be gained in those games where you used the active at appropriate times and turned it off at others. However, there was also a high level of frustration to be had if you realized you forgot to toggle it on, or were sure that you toggled it on only to not have it actually be toggled to active.

Trying to think of other toggles in the game. The two that come to mind are Cho'Gath's Vorpal Spikes and Amumu's Despair.

I don't think the same "weaker earlier for more power later" scenario applies for either, though it is damn frustrating when you toggle them off in the flurry of battle.

Despair is especially hard to tell if it is off since it is a ground effect that is easy to lose track of in a scrum. Though by the same token it is kind of unfair for opponents because it does damage over time that is somewhat non-obvious beyond the fact that Amumu is standing next to you.

Sometimes I wish they had those abilities set on a double tap to turn them off.