The answer has to be as vague as the question: addons
have the potential to make the game run more slowly than normal. There are three general areas where the impact might be felt:
Memory OFP assigns some memory to new addons. Having too many
might cause problems, but the
-NoMap command can help if OFP refuses to start or complains of being "Out of Memory".
Visual complexity Some addons can be so complex (or use many large textures) that the game has difficulty drawing them quick enough, and so the framerate drops.
Scripting Used to augment units behaviour and appearance this causes more work for the processor. Again, if it can't keep up the framerate suffers.
Addons used in moderation shouldn't cause problems except on the weakest of systems (less than 1 GHz processor, etc), but still:
- don't have active more addons than you need: use modfolders
- keep your missions sensible:
200 v 200 is going to cause problems even in vanilla OFP
- remember that OFP is now 10 years old and cannot make use of the latest hardware (multi-core processors or graphics cards)
In short: know your limits.