I use it all the time. Flying a constantly changing road construction site- the base imagery is outdated (where I am working it is at least a year old- so doesn't show any construction progress at all). I have updated imagery (from my previous flight) in google earth so I can trace areas I want to re-map quite accurately- then save KML and upload to DD. Alternatively I can output polygons as .kml from my survey CAD apps eg. using design strings and use that in DD also.
example- base imagery is like this:
current imagery looks like this:
Without this function I would often just be taking a "best-guess" at setting up flight paths- and would often either fly too much area or miss bits in some areas.