Depends on what you're doing.
Walking, driving, running, boating, flying - what?
(won't work well for scuba diving, caving, or riding subway)

When hiking I run it off car power on the way to trailhead then mark where I parked the car. This is the single most important waypoint I'll take all day.

I may get mine out to mark a trail junction or something of importance but mostly it rides in its pocket.

Carrying it around like a tri-corder is a waste of batteries unless you're very close to some coordinates you were given (such as geo-caching). Read about the repeatability of GPS coordinates so you know why you aren't standing in your old footprints the 2nd time....

I've programmed hotel and business sites beforehand when doing business travel.
I've programmed a flight path I wanted to follow (tour of extinct missile silos in Colo. and Nebraska) when flying light aircraft.

I've plotted a wreckage debris field (somewhat questionable in terms of repeatability)

Lots of fun stuff you can do.

See http://coloradowreckchasing.com for more fun ideas.