I use Garmins fairly regularly for work and could see how they would be nice for serious detectorists. Usually I just use them to mark points or to determine area, but like Flipperfla said, you can mark points and name them and depending upon the accuracy (which your GPS should show), they can get you back to within several feet of that spot. The breadcrumb trail could be nice if you're walking a grid pattern because you'd be able to see areas that you might have missed. A GPS can also come in handy for getting back to your point of origin if you're studying old maps and getting pretty far off into the woods in an area that you haven't been to before.
I've used the breadcrumb trail to get myself out of a strange location on a circular knob in Kentucky. I've got a really good sense of direction but a forester who was leading me to the spot said that it was the only place that he'd ever been turned around. I turned on my GPS at the truck and several of us hiked to the site. There was a circle of stones on top of the knob and he thought that it was likely built by native Americans but it hadn't been examined. We accomplished the work that we set out to do and he told me to lead us back to the vehicles. I started taking us back the way that I was sure that we had come, but as we started down the hill, someone asked if we were heading the right direction. I and another fella said yes, but I checked the GPS just to be sure. Looking at the trail on the GPS, we were heading off of the hill in a north-westerly direction which was the opposite direction that we needed to be going (SE). After some disagreement from the group (a few thought that we were going the right way), I showed them the GPS trail showing how we'd come in and which way we were heading. I used the GPS to circle around the knob along the contour and used it to get us back to the vehicles.
Three of my colleagues got lost at that same site several months later, got separated during a strong storm and hiked out of the woods in the dark (that was a funny story...). My friend said that he wished that he'd used a GPS for that trip.
Kindest regards,
Kantuck