I've had a h/w faced ply floor put down by a pro. He did any trimming of the boards round the edges so they were hidden by the skirting, meaning that the factory cuts were used to give perfect joints in the middle of the room. I have dyed and varnished it and am pleased with the results, I am happy to have it on show with a few rugs (sadly he has now given up the business).
I am doing the bathroom in ply myself, and bought it at a higher price from a place that cuts to order using their enormous upright cutting machine. I have a few cuts and trims to do, e.g. where walls are not straight, and am mostly hiding them. However slow and careful I am, I can't get perfect cuts myself (I am not very good at woodwork). Luckily the bathroom is quite small and I have had the pieces cut so all short edges are on joists, except that I have one nog under the basin due to an alcove. I could not possibly put in tongues myself.
I previously did the kitchen in spruce flooring ply, and although it is easy to hide cuts under the units and edges, the face finish is rather poor and unsightly, so would not be suitable for stain and varnish even if I'd wanted to.
IMO the time saved, and quality of the job, repays the extra cost of having the pieces cut for me, and is not much when I am just doing one room at a time. It also makes them easier to carry upstairs.
BTW if you look at the edges of the boards in the merchants, you can form an opinion on whether the cores are gappy or made of little scraps. As Job says, some stocks are better than others. Mine does have a "best" side which is OK as long as you check before cutting or fixing.
