I think it depends on the teacher. Some of it may be useful. Some of it (e.g., twisting the lumbar spine) might injure you.
There is a bunch of stuff on mobility / stretching on this site.
I used to do a Bodybalance class (weird lightweight blend of yoga, tai chi, pilates). more of a mental deload than anything else. i found i got more out of 5-10 minutes focused work myself than out of a 60 minute class where a good chunk of that was focused on crap i didn't want (e.g, sit ups which only aggravated my hip flexors / neck).