Collision budget - what is it?

What does the collision budget exactly measure? It seems that some items contribute to it more than others and it isn’t size related. Primitives seem to be less collision-intensive whereas some of the accent/ceiling pieces contribute greatly. FX don’t contribute, but to my surprise Sound FX do. At the near-limit and discovered it’s a hard limit so just wondering if anyone has any information!

I would also like to know this. I have never made it to the top.

I actually managed to get over 100% by leaving the game and coming back. It was definitely a hard limit before i did this - i was unable to place anything other than invisible barriers and invisible lights. Would be great to find out exactly what it is!.