You need to understand mapping a little.
Nearly all GPS receivers will display a track log. This is just a path of where you've been moving, and it is just a straight or curving line with no background. You can generally zoom in or out, and you can see where you are now with respect to anything else that has been saved, such as waypoints. Waypoints may be landmarks or places that can be described within the grid reference (e.g. lat/long). So, seeing where you are now and with respect to your track log, you can guess which way you are headed, and if that is toward your target waypoint. Waypoints can be saved on the fly when you pass, or they can be picked theoretically off a good topo map and manually entered in. This was the way that many GPS receivers worked in 1997.
Starting ten years or so ago, some GPS receivers had a map database installed. The map database might be only streets and roads (for auto use), or it might be topographic (for hiker use), or it might be marine (for yachts), or it might be aeronautical (for pilots). The map database forms the background for the track log display mentioned above. A few products can hold multiple database files and can be switched. A few products just kind of mixes all map data together for display. If there is a landmark shown in your database map, then you can do a GOTO that landmark. That will display a vector with distance and bearing to the landmark.
So, a mapping database will generally require a good color display, and that burns a little battery power. It will require a faster processor, and that burns a little power.
I've been using these things for 16-17 years now, and I've determined that I need to plan the mission on my home computer using TOPO!, then transfer the critical waypoints to my handheld GPS receiver, then print out a custom color map for the area of operation. Then I carry only the handheld receiver in the field. I no longer work with permanent GPS installations.