It depends, to some extent, on how much hammering the boat is likely to have to take.
Two reasons to do it. Reduce weight, and reduce expense. To fairly good reasons actually.
In a multi chine boat you may as well just glass the whole hull. Too much taping and feathering.
For a single chine hull, and especially if the deck is one curved sheet, if you are using 4mm ply, it can work out well. Good marine ply is tough.
When epoxy saturating the ply, it is a good idea, on both sides, but especially inside, to give the first coat of sealing epoxy a good blast with the heat gun to get it to sink well into the timber. This way, even if you scuff down to the wood over time and abuse, it will still be water resistant, even down into the grain of the first layer.
Of course, adding glass will increase panel stiffness, but the chines, keel and sheers should give ample stiffness along the length.