The selling point of the deployment buckle is the convenience it offers, so it’s understandable that most folks never want to deal with unbuckling it.
I prefer to flatten my bands out between wearing them and that’d require unbuckling every time. Bending the bands for a moment is fine—leather is elastic—it’s the continued stress (like from leaving it buckled) that reduces it’s ability to “bounce back” and wears the leather down permanently. To avoid this it needs time to rest and somewhat return to its original shape.
Hermès recommends storing the bands in their sleeves to do this. I go a step further, laying them out with a heavy towel folded over and that’s how my collection can keep looking fresh like this:
Of course, do whatever you think is best for you. Just know that if you look for used deployment bands, you can easily tell which ones were never unbuckled or stored properly.