Path nodes

[palistov]

I've never had any lag from an abundance of path nodes. I've used over a hundred on some of my levels with no effect on performance. But your "too many" might be different from my "too many".

As mentioned in the wiki article Your Computer posted, physics overload can cause some major lag. If you have lots of objects falling, or lots of objects that collide but have physics active, you'll experience some lag.

Another thing I've experienced lag with is shadowcasting spotlights whose FOVs intersect or overlap. If you're using spotlights to create a realistic lightscape, make sure you don't use more than 2 or 3 shadowcasting spotlights. Better yet, do what I do: avoid having lots of objects which should cast shadows near light sources, and/or vice versa. The less shadowcasting spotlights you can use, while still making a convincing and realistic lightscape, the better.