A lot of times, flash works best when shot at ASA 400, for multiple reasons.
The biggest worry when shooting nighttime flash is that on close-up subjects surrounded by a lot of "night", that the flash will "see"all the black, and will therefore blast out a lot of extra light, and cause massive over-exposure of close-range people and objects. This depends somewhat upon the sophistication of the camera/flash combo, and what kind of metering mode the flash is in.
If you have a high-end, TTL flash that goes with your camera, you're probably okay. Something like a night-time homecoming event...is probably best going to be shot with a flash unit, from 10-15 feet distant. The best tip is this:arrive at the area the event will be held at, and take a few test shots, of the exact kind you will be making...and use those as a guideline.