I can't imagine jumping in the water and trusting that the computer is going to come
on. You turn it on before you hit the water so that you can verify that the batteries are
ok, your nitrox is set correctly, etc, etc. I don't have a phobia of my computer
failing mid-dive so once it is on and working it is probably going to stay that
way. Electronics are most likely to fail when they are first turned on. A dive
computer is more likely to fail by being smashed around in your dive bag between
trips that riding around on your wrist during a dive.
I just seems like a bad idea to not check your gauges until after you are
already in over your head. That goes for analog and digital gauges of all sort.