Having a tempo display of songs would make it easier to make good song choices when creating a play list and controlling the vibe of the night , having it there also on the night you can also instantly see if you are keeping the energy going or you are slowing down without having to read song titles and remembering how the song goes , when you are concentrating on the moment you don't have time or the brain power to quickly make next song decisions while singing, engaging with the crowd and playing an instrument,, a tempo display quickly shows you which way you are heading.
Also, Blank, No tempo setting in a song means you need to enter your tempo setting, its an easy way to see which songs you haven't entered this setting.