Do you mean inverted? (events with an X next to them?) That just means to only trigger in the opposite case (eg: if myVariable = 1 when inverted becomes the same as "If myVariable is not 1"). You can right-click an event and invert it.
Not the inverted condition.
There is a 3rd type of event, which is the FAKE triggers.
See: scirra [.] com /tutorials/598/optimization-and-tle-top-level-events/page-2
'->On Collision' is a fake trigger for example.
See: scirra [.] com/forum/better-to-use-collision-or-overlap_p575390?#p575390
Ashley I think this matter is crucial to know specially for mobile performance even if it's just a fraction. This might alter/rework current worksheets for those who want to deal with false triggers and want more optimization, which is not a worry to those who are willing. Simply retain or improve. It's good to know, it's already in the tutorial, it just needs more exposure. A dedicated advance article or a mention in a more technical section of the manual will be nice.
I still have a lot of speculations about this, I'll just save it for now. I'd like to know your thoughts.
Edit: I can't post links yet, need 300 rep. I apologize.