Hickry,
A shave horse is not a must, a vice will hold a stave better any day of the week.
Some of us just like the shave horse, something to do with traditional maybe.
I use the shave horse because, I really enjoy my back hurting! No, well, maybe...I like it because I can get out under the huge Osage shade tree and peel bark and sap wood, then flip the stave on the side and shave a profile.