I leave it on all of the time. Most of my driving is in town stop and go traffic. The Econ mode cuts overall power by 4%, except for full-throttle. It makes the Auto-stop more aggressive. It shortens the AC compressor cycles to 'just' enough to do the job (unless it it really hot out). It also smooths the throttle input. The CVT is re-mapped to keep the RPM lower at low to mid speeds. So it really effects in-town more than highway.
Knowing what it does helps figure out when you want to use it. If you want efficiency, keep it on. If you want/need all the available power for more demanding driving, turn it off. So now you can obsess about which MID screen is most useful

(my favorite is the instantaneous MPG screen). After about four months I really enjoy mine. Oh, welcome to the forum