mechanics: R2 stepping in after rally
 

I had one or two partnters do this in HS but I see this a bit more when watching college matches(been watching a lot of the big 10 matches on youtube)

After the rally, the R2 on some points steps up towards the sideline when making the signals. Looks its done only when the R2 was on the fault side but its doesnt always happen.

Sometimes the r2 goes steps back instead.

Whats the formality on this?

Or am I just watching r2s that just wander around?

There's no specific reason there. A lot is just situation dependent, like if there was movement toward the pole needed during the rally, if subs or a timeout might be anticipated, etc.