I try not to use them since I like the challenge of think up a team plan but if I've tried enough times, failed and am close to a win or in RL I am on a time limit I use them. Last Nero fest was a big one. I think for about 10% of all the battles I use at least 1 CS the last battle I remember using 2 to 100% NP on 2 Servants for a last chance hope of victory. I normal, for tough story battles, mostly use the 3 at once for team revive or 1 for NP charge. I don't think I ever used one for HP though.