I think you have to play it by ear. As a single hander any help is welcome but I usually do some of the work, even if they suggest I stay on board.
If they have two crew off the boat I stay onboard - after offering to help.
If only one crew on other boat, going down I close top paddle (my side at least), if open, then open bottom paddle my side, before going back onboard. If they want to open both bottom gates, I suggest opening one gate on their side (preferably landing side) and they can go out first, leaving their crew to shut the gate.
Going up, I start to get on the roof, windlass in hand. Usually they will say stay on boat, so I wait until I can step off roof or stern, close paddle my side. If I go out first go on to get next lock ready. If they go out first I suggest crew gets back on and I will shut the gate behind me.
If they want to do it a different way I go along, even if it is obviously slower - I am never in a hurry. I have shared with a few boats where it would have been much quicker on my own.