I think there should be a limit on how many times you can block,
just like with healing. This will prevent users from simply using
block the whole time, or preventing the end of a battle they can't
win.
Basically it is to stop block trolling. I think it should have more
(way more) uses than healing, but I do think a limit is needed.
But in battles where one side physically cannot win (a ghost and
other type vs a pure normal type for example) blocking only
prolongs the battle unnecessarily.