Like Alder, I've started them both ways as well.
Now, I don't bother planting them because they come up
volunteer all over. I'm finally managed to get rid of them in a couple of areas where they kept coming back year after year but I didn't want them any more. They send runners under the soil that pop up next year as new plants. Once established, they are hard to get rid of. We don't have a freeze, so they grow 12 months of the year.
I've found that the easiest way to start new sweet potatoes is to go out to the sweet potato patch (in my case, on a hillside under my figs and avocados) and just hack away at the vines. I use a set of hedge trimmers. Then I take the 1 to 2 foot long pieces of vine and toss them into a 5 gallon
bucket. I fill the bucket with 6 inches of
water, set in on the shady side of the house, and leave it for a week or so. All those vine cuttings quickly spring roots and I have all the slips I'll ever need. I give them away to people who want to start SP's in their own garden.
I mulch my soil heavily with
wood chips at least once or twice a year. I generally just bury the sweet potato vines because there are so many of them back on the hillside. They just keep pressing up through the chips and growing. What is beautiful is that the soil under those vines is amazing. Black and crumbly and beautiful. The sweet potatoes help convert all that wood chip biomass into dark crumbly soil. The sweet potatoes that do not get eaten by me (probably 90% of them go unused) get eaten by various soil biota. We get those green fig beetles, and I think that their big fat white grubs are under the soil in the wood chips, feasting on the sweet potatoes. There are more than
enough to go around.