I would love to warm-up BEFORE I warm-up with my opponent... its just not realistic most times:
a) if you are a visitor for a league match, it doesn't work too well to warm up at your own club, then drive 30 minutes to the match club
b) show up to the visitors club 20 minutes early and expect to be allowed to jump on a court... if there is one open... to warm up with a team-mate
c) warm-up at own club for home matches... if there are courts open maybe, but usually not
d) warm-up outside in northern climate cities during Nov-March? Not likely.