Google limits plugin users to 20,000 data pulls per day. If you run into this limit, you will observe the following error: Service invoked too many times for one day: urlfetch.You can read more about this in the Google documentation.
When sharing sheets, be advised that the URL Fetch Limit counts towards the owner of the sheet. Therefore if you share a sheet, it is recommended you share it in View Only mode in order to reduce data pulls counted towards yourself.