Cleaning aid across a roof is well harder than leading in my opinion. And not something that you think of practising in advance. Ideally I think you want to be able to transfer your ets to the next two pieces and still easily reach back to take out the piece you need to clean. If they are too spaced you end up having to lean right back which uses up a lot of energy. Also if the piece is not straightforward to remove you can end up getting it stuck with all your swinging around. So the idea of the second plugging in spare gear to fill gaps that have been back cleaned by the leader or placed by one of larger wingspan makes sense. Interested to hear what m9 has to say on the topic.