Aswering to the above question is simple,
Lets go back to our basic. When we learned during our open water , our instructor told us to plan our dive , not dive then plan. So basically dive computer is best to put as our back up unit . We should not depend on it as our important tool of our diving life.
Secondly, in PADI Dive rules, that if you dive using a computer, you need a miminum surface interval of an hour! So we stay up for an hour is the minumum when u dive with computer!
I dont know about other agency .. Cheer
No offence to anyone . ya !!