Power meters are used to get a better measurement of effort, usually more accurate than purely heart-rate. As heart-rate can be skewed by caffeine intake/fatigue and many other small things.

I get the gist of it for training, but not exactly for racing. Maybe for pure TT/Hill climbs is makes sense if there isn't any other competitors around. But for something like a crit/road race, I don't see any benefit.

If you need to get in the pack, it might require you to put out 400w for 10 seconds. If you don't, you will be dropped and then you have no chance of placing competitively. Some people with a power meter might be afraid of reaching 400w, as they know they will blow up at that power. But you definitely need to push to make it into the group.

To conclude, sometimes you will need to make a certain power in a race, and I think a power meter discourages one from pushing his limits in fear of blowing up.