The reason for seeing the band and signal details is to find the best position for the router. I have used hotspots with this info and it is very easy to compare the service at different locations around the house and thus find the best location for placement. Sometimes moving the hotspot a few feet or even inches makes a big difference. There could be wall insulation, beams, etc. blocking signals.
Running speedtests is useful, but it takes more time. And speedtests vary. So you could move the router, see a lower speedtest, and think it is a worse location. By seeing the signal, SNR, etc., you may see that the new location is really better. Several speedtests over time may confirm this, but is more difficult and time consuming.
Seeing the band also helps, since you are able to better compare apples to apples. A weaker signal may force the router to shift to a lower frequency. It may appear better, but again, a location at a higher frequency may actually be better since the signal is stronger. Locations with stronger signals across bands also provide more flexibility for reliable service.
Lastly, placing the router in the best location helps both the subscriber and Verizon. Weak signals increase the airtime to transmit data as well as providing slower speeds. This slows down the network for everyone.
It seems to me that this feature is even more important on a home LTE router which will not be moved much once it is installed. Bad placement will result in poor performance for a long time.
