Why does CrossFit use Kipping Pull-ups?

It's no surprise that CrossFit would utilize kipping pullups in their program, as they also do likewise with athletic exercises like Olympic lifts and even some Olympic rings programming too.

Besides being a somewhat more "athletic" movement (compared to strict pullups), kipping pullups also have the advantage of being able to recruit more lats in people with high-lat insertions too. Namely, since they are not doing a strictly "vertical" pull (rather, something more on the side of a suspended inverted row -- with elbows more to the front rather than to the sides), this could put their lats in a more advantageous position to help out with the movement. So, unlike in a regular/strict pullup, those high-lat-insertion folks will feel it more in their lats than in their forearms.

Note: I'm not saying that forearm development is necessarily a bad thing. Different people have different biomechanics, which could significantly change which muscles will get more recruited/focused/emphasized than others for a given exercise/movement.

*Edit: here is an example of high/low lats insertions (although "origin" could be the more proper term!) https://forum.bodybuilding.com/showthread.php?t=167582371&page=1

The primary reason for Crossfitters to use kipping or butterfly pullups in workouts is because they are faster and require less energy, enabling you to complete more rounds and finish faster.

Strict PU's are wonderful for building strength. Unless you can do strict PU's, it's best not to attempt kipped ones because you can injure yourself more easily.

At our box, we have do strict PU's for the strength part, but are free to complete them in any way in the workouts. I personally like this particular approach because it allows you to build strength while completing a variety of movements.

The kip is not legal everywhere.

When I was in the Marine Corps (1988-92), the kip was allowed, and I used it because I did not have the upper body strength to complete 20 dead hang pull-ups.

Since learning the kip is no longer accepted in the Marines, I stopped using it to complete my pull-ups.

The kip is a good, all over body workout, and it can still exhaust you. My guess is that is why these CrossFit courses are using them. These courses are not designed to make you powerful and strong, but rather they are designed to get you into shape.

Yeah, you could injure yourself. You could also injure yourself by slipping on a wet floor in the bathroom at work, but you still go in there for your business. Right?

So, now it's time to show your buddies you can do 20 pull-ups. Are you going to kip or use dead hang? If you kip, they are liable to say, "Dude, WTF was that?" If you do a dead hang, they might say, "Bro, your chin didn't go all the way over the bar on Number 18."

This is sort of what others have said, but I just wanted to put in my 2 cents.

I'm not a professional trainer, though. I'm just someone who's been working out for 25+ years.

I look at it as, they're competing in a sport with a completion criteria of chin-over-bar for reps/time.

If the participants understand that they're taking on a certain level of risk of certain types of injuries training for this type of competition, then that's their business.

People risk straining muscles kicking soccer balls too, but they accept the risk because they want to participate in a competition that involves kicking. A particular coach not being clear that this is a reps-for-time technique and not also teach correct strict form for strength training, that's a diff issue.

Re: talking to people who may be perceived as too gung-ho about crossfit to critically examine their training, I would refer to 'Becoming a Supple Leopard' by Kelly Starrett (who obviously has some serious cred with crossfitters). The very beginning of the first chapter has a good discussion about the dangers of 'task-completion obsession' that is perhaps helpful in getting people to examine when it's appropriate to take "game day risks" for one more chin-over-bar and if they really want those risks to be part of regular training also.

I think you should approach them like you should approach everyone who does something in a way you don't agree with (or don't understand): with respect and without prejudice.

In my opinion (not a crossfitter): Kipping pull-ups are a different exercise than strength focused pull-ups. They focus primarily on explosive movement and the clever use of inertia.
The goal of crossfit, as I understand, is real-world application of the movement. For climbing a normal pull-up is useful, but you don't always want to do something elegant and clean, but simple and quick and just jerk your body up.