Well, for me gps is useful for tracking pace and distance and it also brings bit of safety aspect, since it can show me way home if I happen to get lost in forest.. Knowing this, I don't need to hesistate if there's interesting looking path to explore or when running in darkness at night. It's also a lot easier to have personal records on different distances and try to improve them spontantenously.. When running fast, it's interesting to know how fast and when running far it's nice to know how far. And it gives motivation to go a bit farther.