It would save a lot of work and time but you better have a good size area to work in if you are going to lay out all the pieces and glass them before assembling.
The down side I can think of is when you go to trim something , it is a lot harder cutting threw the epoxy and glass on the wood then just the wood.
Some folks have done it that way and they said it is a lot easier to glass the inside by doing that.
My first post that I made on this forum was asking about doing the same thing. It could be done on a simple boat like a pirogue, but you would still need to tape the seams on both sides. By the way, I didn't end up doing it that way. I ended up first building Matt's Touring Pirogue-T instead.
My first thread is here: http://www.neilbank.com/phpBB3/viewtopic.php?f=11&t=2505
You are going to glass the sheets then cut them, stich them together ,run a filet then have to use tape to go over the seams.
id you do it the way we do you can cut out the taping of the seams ,your cloth will take care 0f it.
Well, this boat is going to be a hard chined boat, e.g., a box boat, jon boat. I'd like to put the hard chine on the exterior, but I see your point about doing twice as much work for half the effectiveness.