So far, on my Accor hotel check in, I have no issue with LCAH priority lane.
Empty and the staff promptly handle my check in when I queue there
Maybe I'm lucky =D

At other chain, (SPG now become The One Program Who Haven't Got Name Yet) at some hotel, the staff did enforce the priority queue and ask non members to move to normal queue.
When everyone queueing at normal queue however, they keep priority lane unstaffed. the staff only comes out when someone queueing there.

At the hotel with Executive/Club Lounge, The staff straight send me upstairs for Lounge check in

Then on hotels without lounge, when even the priority queue is pretty long, the staff will ask me to wait at lobby sofas and they will get my ID and card to process the check in