ok, i did some checks, here's what i found out:
images show measurements and what events trigger how:
here's a short explanation - if you have a object that collides with something - if you check vs family - it checks for all objects in that family each instance on screen - for example red and green squares are 7 = so checking 1 blue vs 7 objects (2 are in family, but red has 5 instances, and green 2)
if you add "on collision" - it checks for collision whole time, but if you want additionally to check if it's collided with something and nothign else, adding not overlapping under it won't be checked until collision happens. when using overlapping - it checks the same thing - if there is collision / overlapping, but triggers every time there is, not just once like event trigger on collision.
and finally the sexy part - if your object moves (for example with bullet and some speed) - and you want to check if he overlapps when it stops, put bullet speed = 0 first, because then collision checks do not happen until your object stops - after that speed = 0 and checks activate.
there's probably much more combination but these are some common and happen the most, so designing your game for reduced colly checks should be taken with much care, hopefully someone will find use of these graphs and images..
if anyone has questions, pm / write here