Well unless they are caster and have heal or regen on ff7 wouldnt be able to use more then once the limit break per battle. After all it take serious beat up and twice the beating needed = overkilled.

For ff8 they could use it a few time but then it kinda make it unfair to use it a few time so i say it should be max once.

And for ff9 it take serious beating or situation involving big emotion so it is not likely to happen twice in 1 battle and it should be limited to be able to 1 trance per battle anyway.