I once paid Al Weber a fee to critique my portfolio. He loved the work but scolded me for having some mounted on black board and matted with black board. He said while it's currently trendy to do that a museum curator would consider it amatuerish. He also scolded for having the telltale format edge be included in the photo. Apparently the pro's aren't impressed that you have made a contact print from an 11X14 neg and left the edges on to prove it
I would add that in my own home, more than half the photos are on black board or matted in black, just because that was what pleased me most.