Bycicle computers are much more usable as only for showing the speed of your bike. For example with the right sensor it is possible to use them as a fuel meter, which shows you, how much fuel has already flown out of your tank.
With another sensor and module it is possible to check the temperature of your engine oil, or water or just the surrounding outside temperature. More about the possiblities using a bike-computer you will find below on the several links: