Buy the Subsim Almanac
Along with other stuff there is a great artical about a guy who played
several patrols all in realtime. His computer ran for days on end. Wish I could remember his name but I'm away from home with no book to hand. Anyway this guy immersed himself completely, named all his crew, discussed the war progress with them, caught lice together, shared left over food with friendly sailors near home port, you name it. A cracking read. Yes he left it running while sleeping, even when he was using stock SH3 before the fatigue mods arrived. Had an alarm set to wake himself up to organise shift changes! Yep total immersion (don't think he sat in a cold bath tub though).
Personally when nothings happening I have TC up at 1024 (the most my laptop can handle). I have'nt got enough time in my life to spare much more than a few hours a week to SH3. So I try to make the most of it and enjoy convoy action. But it really is, as many have said, each to their own and very dependant on how much free time they have to spare.
IMHO use of TC does not effect realism.