When you say limit. Do you mean limit the frequencey? (so you can't have something refreshing more than once every 10 minutes say) Or limit where people schedule stuff, so you aren't running too many refresh operations at the same time?
I'm not sure you have any controls over this via the config but you can run queries / reporting to show these things so you could monitor and "alter" stuff that has been scheduled.
So I'm not sure if that would help