I save my Card Reveals for 3 occasions:
1) For Event Gacha
2) For Guaranteed SR gacha (since I don't have all SR cards from there yet)
3) For the final step in the "find girls" daily, when I manage to already get one or two of the required 3 girls. This is only useful if you're after Ex-levels for specific girls, and thus only if you already unlocked Ex-levels. Even then, I make sure to keep a bunch of card reveals for the Event Gacha, since that's way more important than Ex-levels, so I only do this when I still have more than 10 card reveals anyway.