A lot of people prefer to keep the C+ upgrade request turned off in the profile and to enable it for individual flights only if they've checked the seat map for nonmiddle C+ seats just before the window opens. Of course there's still the risk that you could say OK to a C+ upgrade and see a bunch of unpfrades clear at the same time when the window opens so that no aisles or windows remain to enable you to switch out of an assigned C+ middle seat.