Yes using a cutter will use more fabric, how much more depends on your skill with using it. And some places are more generous than others when it comes to putting kits together. If the kit is from Connecting Threads, I wouldn't hesitate to use my Go! if I had the right dies. From Craftsy or a few other places? They're squeaky tight in the amount of fabric they give you so no I would cut by hand.
Cari