Joining a client in the shower could mean an early pop .... and then it's over.
One reason to stand back while they freshen up.
It could change the whole dynamic of the intended purpose of the session.
I HAVE joined some ... who are ATF's .... and I know they've mastered how to hold back.
It all depends on the guy .... and what they want to accomplish (as in getting a true bang for their buck. No pun intended)
As with everything else, you feel it out and make a decision.
My sniffer is spot on. If they walk in the door "needing" to shower ... I offer it to them. No worries.
But .... If it's just nastiness from an unkept lifestyle ... I will turn them away .... shower or not.