Due to the aesthetic reason Vaughn mentioned, I continue to drymount the prints I sell. I prefer to have a flat, free-floating print and hate overlapping mats. Unsold prints are kept unmounted in an archival box until they have found a buyer. If a gallery insists in unmounted prints, they get one from the box, but nothing is as flat as a drymounted print.
I think the 'if the mounboard gets damaged' issue is overrated. I didn't have a single case in 30 years. However, I had a few cases were the glass broke and the print was damaged.