EVENT mode is very data intensive, so there are some limitations on how long UVOT can collect data in EVENT mode due to limitations in the spacecraft data storage capabilities, and the telemetry bandwidth between the UVOT-and-spacecraft and the spacecraft-and-ground station. Full frame event data can only be obtained for short periods of time. In general, the smaller the window size, the longer event data can be obtained.
Most UVOT IMAGE-mode observations will be taken with binning in order to conserve telemetry. binning can be requested if there is a strong scientific justification.