In a nutshell mainsail shape is more easily controlled with a fractional rig... it's easier to 'shift gears' without sailchanges. For a given size a fractional rig provides lighter, smaller headsails (jibs and spinnakers) making handling essentially easier, with lighter loads..d
But there's more... check the thread..
__________________ ".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)