Here's an idea to think about...
You may have noticed today's warm up was pretty extensive. When you look at a workout that has double unders, box jumps and burpees, you could say those are "warm up" movements, so why take all of the time to do a thorough warm up when we could just get right into it? The idea here might actually sound pretty simple.
You have within you a metabolic engine. There are many systems and processes that shoot into action when you begin a warm up, and when you workout this metabolic engine is working at its peak to supply the energy and create the movement needed for the exercise. But the key here is - what happens when you are done working out? What is your engine doing? This is one of the main differences and values of CrossFit training. When you have a workout that is very metabolically taxing, like a CrossFit workout, your engine is still revved up and using energy throughout the day.
Take for example walking on a treadmill compared to sprinting 800 meters. Let's say you burn 100 calories walking a mile and the same amount sprinting 800 meters (I have no idea if these numbers are accurate). Calories in Calories out would say this is the same thing, but the main difference here is the stimulus you have put on your metabolic system in the 800 meter sprint. Now your body will be going through an adaption process long after the effects of the mile walk have warn off.
So back to the point, why such a thorough warm up? Because this is how you capitalize on using your metabolic engine. To be as sufficiently warmed up as possible - pushing yourself hard (relative) in the warm up is going to put your engine in a position to not only be able to output to the extent you want during the workout, but you will also reap the benefits of the workout long after it's over by having your engine more active.
Lastly, and we've heard this a lot, "I don't want to use all of my energy in the warm up." Two things. One, sometimes the car coughs a little bit when it starts. Warming up can at times be the hardest part of the workout. You just got out of bed, laying down for 8 (hopefully) hours and now your asking your body to get down and up really fast. It takes time to get your body going (another reason for longer warm ups). Be patient :)
Secondly, if you truly feel like you are already warm and the warm up is still going, you can cruise it. Throw it in cruise control and relax.
Here's a picture of the super fun 9am class this morning.
1 min: Double Under
1 min: Burpee
1 min: Box Jump (24/30in)
1 min: Rest