What is the purpose of the daily reputation limit?
The only one reason I could think of would be someone quickly getting an incredulously high reputation and accessing moderation tools to damage the site/content in some way.
This question What is the reasoning behind the reputation cap? on Meta Stack Overflow is probably the definitive one.
There are several reasons including the one you mention. Another is to give you a reason to stop using the site - you've hit the reputation cap, there's no need to keep posting.
I'd say that stackexchange is something like drug... Better than drug
Cap "forces" you to take a break, and do something else. When I reach cap (+ 100 more reputation) I have really no reason to continue posting, as ChrisF said