I've had this belief for awhile now. But is it true, especially in larger assemblies? Or am I mistaken, and it would actually save processing power of the computer if I just deleted all the mates in an assembly, or just locked everything in place? Maybe even take the time to fully define sketches? And change all sub assemblies to rigid instead of flexible.
I'm working on a 2000+ component assembly, and even when all the files are on my computer it takes over 5 min to load. 25 if downloading from the archive.
EDIT - I marked this answer as correct as it answered the orgianal question. But there is a freeze-bar technique talked about that I'm using.