I see a lot of friends juggle with some sort of internal battle between being off and on with this stuff, and then there are friends who just slowly "cruise" with it without affecting them.
So what's the point? I don't like or comment on anything on Facebook. I don't post anything on Facebook. I just open it up to mindlessly scroll. I don't need that. I have other sites that I believe are better uses of time to mindlessly scroll (this site included).
From my perspective: I'm a photographer and there are DM photography critique groups I wouldn't want to miss out on. Groups with contributors that have seriously improved my work.
Outside the critique groups there are darkroom groups where techniques and tips lost in the digital age are shared -- I shoot analog so I can make darkroom prints (a little non-digital zen after writing code for 8+ hours a day) so re-discovering some of these techniques has been vital to improving my printmaking skills.
I'd imagine there are probably yoga technique groups that are similar. Critiques of form and posture, tips when trying to reach that new, difficult pose, scheduling for impromptu classes, etc.
Any tight knit Instagram group of posters has some longer form discussion on the DM end of things in my experience. All people you want to speak with, but wouldn't do so over text message for whatever reason. I've tried multiple times to lift and shift groups to Slack, Discord, Discourse, etc. Never works. Instagram has a tight hold.
Posts are used as blogging tools. Along with fancy pictures of our latest poses, we like to write about the philosophy of yoga.
We also use DMs to communicate, along with WhatsApp, and stories to share random yoga and not yoga moments.
Yogis aren't just a group of gurus hanging at the top of a mountain :) Obviously, there is a conversation within the community about the usage of social media and addiction thereof.