[fatrachet]

The display is used for a lot of things, not just for speed. For example during saturday qualifying drivers usually have the time difference of their laps to the leader on the display, and it gets constantly updated.

It's quite interesting to watch cockpit cams and see the effect any little mistake or different line has on the lap time. You can also often see differences in brake balances between drivers and more on them during the race, can be really interesting if you pay attention to that.