If you have chronically tight muscles like some elite athletes do then yes it's helpful to loosen stuff up significant before you workout, especially hip flexors.
There's no real set rules... I mean I try to delineate some here:
http://www.eatmoveimprove.com/2009/0...ic-stretching/
But it all depends on the athlete and what you're trying to work on with them. He works with Hockey player so.... there ya go