I've only run Deso at high water but have done it both ways and it's kind of nice to be camping above the rapids the first night. Some folks like having a motor for the first 20 miles of flatwater, especially if the water's at base-flow and they are rowing into strong headwinds, or to make better time if there's a tight schedule. Others ardently object to motors on ethical grounds. Some are ambivalent.
Personally, if it were my trip and someone had a quiet 4-stroke they could bring along with little extra effort I'd be glad to have it along even if it stayed in its box for the entire trip. This is not only for the first part of the trip or to deal with stiff headwinds, but also in the event of an emergency evac. I usually tripcost $20 if someone brings a motor for fuel and maintenance.
Others will chime in, it's up to the group's personal preference.
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse