keep in mind that when you are attacking your carriers don’t add any combat die, though you often still want to bring them along in order to soak up 2 hits each. one of the unusual outcomes of this is that the attacker doesn’t much if any combat power (total attack dice) during the first round of causalities because he only loses carriers. This makes the odds calculation a bit different than if you are defending.
If you are attacking, your planes are also more flexible; you can lose all your carriers and they can usually find somewhere else to land. When you are defending your carriers cannot land any planes if they are damaged so you might as well drop 2 hits on them instead of 1, they also are vulnerable to any surviving subs or really anything else (with a defensive combat value of 2). Since your planes can only move 1 space as the defender, you may or may not be able to crash land and so you may feel that you want to keep carriers in case you live (otherwise, the attacker could simply withdraw and all your planes crash for lack of anywhere to land)
The result is that losing your carriers on the offense is an awesome sacrifice strategy, whereas defending carriers are in a much more precarious situation because they don’t contribute much to your defensive power but you also cant lose them all first in most cases….