Its a shame... because most of the time you should. We often need extra light top pull out details and increase the depth of field. Reflections on glass are not an issue if you are shooting correctly (see "shooting through glass" thread).

Once using a flash, its a common mistake to play with shutter speed excessively to to the point where we sometimes corrupt the color of our images by allowing the shutter speed to be slower than the fash. Without these two in sync, extraneous light makes it into the image and can corrupt it. This is perhaps yet another reason to sync the flash with (hands-off) shutter speed and/or let the camera adjust the shutter setting for you (as in Aperture Priority mode).

You will see this plays a HUGE part in fluorescence photography (see the photog column on this topic in my next issue of C the Journal - v1 n2)

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Anthony Calfo