Excellent Question RickN55.
The eTrex SE is the replacement for the eTrex 10, and both are very basic navigation instruments that offer a good value for the price.
Long before todays modern devices existed, if you had a GPSr, it only gave you coordinates, and some would allow you to save a few waypoints so you could plot the direction and distance to them from your current location. For many years, those with GPSr still used good old fashioned paper maps with the GPSr providing confirmation of desired locations to make it easier to pinpoint locations on a map and plot your course.
Digital maps are not required to navigate using a GPSr, they are a luxury. None of the extra bells and whistles found on modern devices are necessary, but some sure are nice to have.
The eTrex SE is for those who do not need or desire digital mapping on their navigator. Many of these users are already using an external map product, either digital or good old fashioned paper, for their mapping needs. Some of us actually find it very refreshing to shed all the 'fluff' found on modern navigators and get back to basics, which the eTrex SE allows us to do!
Those who wish to enjoy modern digital mapping with their eTrex SE still can by pairing it with the Garmin Explore App on their phone, where they can view device data along with a variety of high resolution digital map products, as desired.
Models like the eTrex SE are excellent teaching tools because they allow new users to concentrate on the basics without getting distracted or confused by additional features.
Please reference
An Introduction to using Garmin GPSr with paper maps for more information.
Oh, and if you were thinking about getting an eTrex SE any time soon, maybe wait just a little bit longer.....