Only harm I could possibly see, not sealing brackets on camper. Or somehow managing to back truck under with out noting they are still down. Otherwise a plus, even if you use stands.
I also use the small stands with some wood spreaders, but only on extended stays or parked on really questionable ground. (the since returned camco stands were too short for our camper @17" even with blocks, pictured are my old Reese at 18 1/2")
Though I dislike the movement when offloaded one of the primary reasons I made our "or the like" was for the lifting and lowering of camper. That has always been sketchy on our 'weaver', more so with the extended jack plates. I have 2 pair on each jack, front to back & side to side
When the jacks get flipped out I attached the front to backs, as soon as truck is clear I attach the side to sides. A simple world of difference in camper moving when elevated.
So much so I recently added a fixed pair to rear legs. Though some campers come with lower brackets attached to bumper, our lower brackets are 2' up & the way they are mounted only offered front to back, virtually no side to side resistance and they moved a lot.