It really depends on what someone wants to do with the GPS data.
For myself, I stopped caring very much about the data I've been logging with my Garmin the past five years. It was good for knowing how far I went, and I suppose it can be good for knowing where I went -- but I remember where I went, right?
So, then, what do I do afterwards -- do I show it off? I'm not going to post my routes on Facebook or anything like that.
All my running and cycling routes, then, are just taking up space at Garmin Connect. Maybe, if I really wanted to dig deep into my data, I could see where my slowest sections were and how steep the climbs were... but I just don't care. After doing enough rides, all I wanted to know was my heart rate and the time of day.
Okay, let's say that I'm training for a 5k/10k/half marathon/Ironman tri/Tough Mudder. Am I in the hunt for winning my age group? No, I'm not. What I really want to learn are two main things: what I should eat beforehand (so I don't die), and what I should wear (so I don't chafe). Besides that, running the race is simple: follow everyone else and run until the finish line. If my watch is inaccurate and thinks I've traveled five kilometers when I'm actually 0.1 km from the finish line, am I really going to stop running? Duh... NO.
I honestly believe that GPS isn't a necessary tool for exercising. It's entertaining (which I suppose helps people enjoy exercising), but it's not like people haven't gotten faster without it. I think it's a market created by gadget manufacturers who made compact, low-power GPS chips and wanted to sell them. Basically, consumerism with -- hopefully -- health benefits.