It's habit for me to turn it on when I'm underway(I leave it on overnight on anchor as well, it's a great tool for anchor watch). It's the only ships clock we use as well.

I rarely remember to set the trip but I always have the "odometer" reading at the end of the season. From there I remember one fuel filling this season(gallons), and estimate. Then I had to estimate the days but that was pretty easy as it was a light season.