You don't need a starting clamp, but it does come in handy. Especially when you need a bridge. With a drop weight, you'll definitely need a bridge when you come up short. I have at least two for every machine I use. One is useful, two are very handy.
When I first started stringing, I did not have a starting clamp. After I got one, it was big help. Then I got a second one, and boy it comes in handy.
Machines: Gamma 6004 2-point w/ Wise 2086 & Babolat Sensor Dual