We do it as a matter of course here. Gives us a head start most years and it also makes a dry period in late summer/early autumn less of a problem. We do it mainly to get rid of volunteer wheat in fields that are going into barley, but also to get ahead of the weeds. Usually a mix of glyphosate, MCPA or 2-4D, and triclopyr (Garlon, etc.) to get everything killed.