I have discovered the hard way (luckily with boards that were still with me) that if you do not seal the back of the board, it can warp at various times of year due to humidity. This is very noticable with larger boards. I personally think it looks better if the back is sealed with clear gesso or GAC100 rather than coloured gesso. I have used shellac to seal boards as well but I find GAC100 easier to use.
I am also curious how you would store while drying and before stretching a canvas that was painted while it was taped to a board. Would you have to leave it on the board for a few weeks or longer? BTW I saw a photo of Richard Schmid and it looked like he was paintting on a canvas taped to a board.
There is no issue for smaller paintings because it is easier to use boards, covered or not with linen or canvas and gesso. The reason, i am thinking about and researching this is that I would like to do more larger works but the ones I have already done cause a storrage problem in my small studio. Once you get to larger than 9 x 12 inches, the boards probably should be cradled and things start getting heavy and bulky.