The GPS has been used for two main reasons. The first is when gathering hounds. Its easy to see where they are and to get them back. The second is that the tracks provide an interesting study in how the hounds run, which ones are leading, etc.
The astro and the alpha provide both maps and distance/direction. You can plot points on the map for reference as well.
"I couldn't find my keys, so I put her in the trunk"
I don't recall what make/model ours is, but we just use distance and direction. There are fixture maps in the hound truck and one of the members made a distance overlay, so it's pretty easy (if you know where you are with the base unit) to figure out where a particular hound is located.
It's definitely better than nothing, particularly if the pack splits or hounds are getting too close to busy roads. However, it's difficult to get good readings quickly--the unit freaks out and will swap north and south or flat refuse to update hound locations unless it's stationary and perfectly flat.