Generally acceptable losses for battles in GC?

I'm a total noob to this game and I'm just trying to get a general feel for how it should be played. I can't really get a sense of expendable units are meant to be. I've mostly played a lot of Total War games and WW2 RTS/campaign games, like Hearts of Iron and Steel Division. In those games, units are a substantial investment and experience is an important factor. Generally, you try to build up a very robust army that can survive an extended campaign with minimal reinforcements. If you're trying to play a "perfect" game, a costly victory is often still a reason to reload and try again if you lost too much of your main force.

So far in this game (vanilla and several major mods) I'm finding that it's almost impossible to effectively use corvettes and fighter/bomber squadrons without taking massive losses. Is this because I'm playing my battles wrong, or are they meant to be expendable assets that should be constantly replenished?