The only use of bond scroll that you need to save for, for now, is the board thingy event where there is a daily quest of "do 10 pull" which you can accomplish by doing a bondx10 pull.

Other than that, there is no reason to save bond thus far.

And that event is pretty rare, maybe (hopefully) it have been dropped from the rotation.

Still, given that, you can keep up to 70 of them, rest you can just use. The extra bit of coin will let you get your next 8 gate (or upgrade thereof) just a little earlier, might make the difference in... something. Thou tbh the thing is pretty meh. I've more or less neglected to log on via mini client daily now, I used to do that for the coin and bond scroll but now... just not very motivated.