The Go Plus is a XP and Star Dust accumulating Machine.
I initially bought mine just for spinning Poke Stops on my daily commute to and from work so I didn't have pull over/Park Car to flick the Stop all the time. As an experiment I decided to catch stuff while at work with it than that changed to catching to and from work as well as the stops. I only did this Mon-Fri. On weekends I threw balls manually while at Lures or Hunting.
I documented all the logs through the journal during during a 5 week period with the following results.
749 caught @ 57%
569 ran @ 43%
74900 Star Dust
This was all pre New Gym System update. This was all Dust and XP that I couldn't normally get.
I don't use the Go Plus during work hours but every minute outside of work that I have Pokemon Go running on the Phone the Go Plus is on accumulating the Dust and XP.
The only thing you have to watch when hunting and having it on is clicking until you know what it is as you run the risk of that thing your chasing and desperately want dusting you off.
I never look at the Journal to see what I've missed. What I don't know dusted wont upset me \
As it only uses Red balls, managing the bag space can be a juggle.