We've all seen this warning message displayed when you are trying to add more than 8 points to a collision polygon.
I decided to test if complex collision polygons are really that bad for performance. Here is the test project.
Note, that this test is quite extreme - there are 210 rotating objects, each object is tested for overlapping with all other objects on every tick. That's about 2.5 million collision checks per second!
And yet on my mid-level laptop the difference between 4 points and 20 points in the collision polygon is really not that big!
I'm also working on another project, where people can load a custom image and its collision polygon is detected automatically. As a result, some images might have 200-300 points in their collision polygon. And this still doesn't cause any noticeable performance issues.
Conclusion:
First of all - kudos to Scirra for optimizing collision checks!
Second - don't be afraid to add a few extra points when needed. But of course, try to keep the number of collision checks low.
And finally - I think the threshold for that warning needs to be increased. Maybe show it after adding 15 or 20 points. And I would really like to be able to click "never show this message again" and hide if forever.