I was referring to events in the event sheet that happen in response to something, or they may be called conditions. Instead of constantly testing for something, you can simply create a condition like:
On Z pressed:
If down arrow is pressed Slide
Else
Jump
That way every tick it's not testing for your condition. When you hit the Z key, it checks to see if the other conditions are true, then reacts. That way when the Z key is not being pressed, you are not wasting processing by looking for it.
Some types of events are triggered by certain things happening like key presses. For these you don't have to check every tick. Every tick should be used as little as possible. The more things that run every tick, the more your code has to check for and it doesn't scale well once you start getting multiple enemies, etc...