The purpose of the warm up is to make your system ready to provide maximum power from the start.
If you do your warm up in a controlled environment like a velodrome, you should slowly see your power rise with what feels like less and less effort. Don't know about others, but as my warm up progresses I also get the benefit of a more clear airway (nostrils).
My typical warm up looks something like this:
1.

Damn, those 100 watt feels heavy (body wants to stop and lie one the sofa). How the hell am I gonna do a race averaging 300 watt?
2.

Ok, doing 150 watt and it doesn't feel that bad...
3.

Doing 200 watt and it's still not that bad....arghhh now it's not too pleasant, backing off a bit...
4.

Wow, that helped. Now putting pressure on again and doing 250 -300 watt and it feels ok.
5.

Ok, I know those Chain Gangers are a crazy mob...better throw in some 4-5-600 watt sprints to prepare for the shock.
6.

9 minutes to race start....I'm ready now dammit. Well, have to keep warm, maybe I should do a few 3-400 watt pulsing just to remind the system what's ahead.