Trigger question about performance

I am using triggers to set entire levels visibile and on exit of the trigger box to set it to invisible. My question is it better to have multiple small trigger boxes to set on exit visible or invisible or is it better to have an entire large box that sets the level to visible on enter and invisibile on exit… And what if the level is an odd shape outside of a box? How would i handle large trigger boxes that overlap with each other?

I think level streaming might help you with this.