The way I see it, CV's are a force multiplier for taking bases. You get a friendly umbrella in the form of puffy ack, you have 8" guns that can demolish towns and hangars much faster than upping a set of buffs, you brign GV spawns into play where you may not have one, as long as it's floating you have troops and ord, and you can park it right off of someones base and pump planes into the fight as fast as they can.
Taking these out of combat is intentionally making your forces less effective, if you don't want to lose them, be smart. Pork Ords. It takes 20m to fly around and pork ord at 3 or 4 bases... it takes 12 Hours to sail the crap to where no one can use it, and it's of no use to you. What's the point?
Yes, I can up from any other base I want... but any other base isn't going to follow me to the engagement.