Originally Posted by
Kannai
An early check-in time makes you far less likely to be involuntarily denied boarding due to overbooking. (Having a seat helps too, but check-in time matters.) And if you have status, your chance of a free upgrade is in part based on check-in time.
While what you have said are true, they are not really significant.
AFAICT - UA determines both CPU and IDB priority based highly on status and fare classes. While check-in time is a consideration factor, usually UA does not need to go that far and would be able to pick out the winners/victims just by status and fare classes.