As I noted above, you can now downgrade yourself out of C+ if you don't like your seat. I see little reason to turn off the C+ upgrade option at this point other than in gate upgrade situations.
Here's one reason that I have encountered personally: as GM, select standard economy seat in exit row aisle; at T-72 get auto upgraded to C+, getting the email while in a meeting; a couple of hours later go back to office and log in to find that C+ is actually a middle seat, original seat is taken, and remaining standard economy options are in the middle or in the way back.