KCV is convenient for anyone who is struggling a little with the language and want to keep track of those quests and expeditions.
I think the more important function of the viewer is that it shows you your girl's fatigue/morale level and the time needed for them to heal. Without it you'll be blindly going in and have to wait for god knows how much time, screwing up the whole damn game.
What's more it save lives during sortie because you can check them incase of any major damage if you happen to miss it.
I don't think I can go back to not using KCV anymore.