A new study (1) getting lot's of media exposure has demonstrated that traditional long warm up periods (45 to 90 minutes with several hard sprints) used by sprinters and short duration event athletes are too fatiguing and rob athletes of their best performance.
Instead a shorter gradual 15 minute warm up with one sprint at the end increased performance by about 6%.
Don't scoff at 6%, that can provide a personal best or podium finish. Also, think of saving all that wasted time! 15 minutes of warm up compared to 90 minutes makes it much easier to manage pre-competition preparation.
(1) Less is More: Standard Warm-up Causes Fatigue and Less Warm-up Permits Greater Cycling Power Output