So when you ride your gravel bike, you can see how much of your ride was actual gravel. This could be important to promote your ride among gravel riders... so your friends (and yourself) can see if this ride has a substantial percentage of gravel. This might not be usefull in the US where there is a lot of gravel, but it is a great help in Belgium where you don't find enough gravel for half your ride sometimes.
You can do the same with climbing kilometers when using the gradient map... so you can see how much of your ride was actually uphill.
