[Yehuda]

I always wondered, in these joint exercises, is each side (a) holding back some of their latest tech and tactics, AND (b) noting as much as possible of their “partner”’s?

[OldTCS]

Of course!
But a lot of effort does go into communications, unit coordination, not running into each other, etc. Generally gives a good indication of how poorly everything is going to go if they ever have to do it for real. :)

[MyTwoCopperCoins]

Usually such exercises are meant for non-military ops.

Last year, the USN conducted exercises with the Chinese navy.