If you are on a paid plan, your requests will continue to be served even after you exceed your quota. You should not have to worry about this and your service will not be affected. If you exceed your quota we will simply apply the per operation rate and charge you for this additional usage after a few days.
If you are on a Free plan, you might run into the hard-limits built into it. Free plans have both a daily limit (500 operations per month) and a monthly limit (2000 operations per month). If you think you might hit those limits, we recommend that you consider subscribing to one of our paid plans.