Elevation gain, shown on the maps like Ride with GPS, will help determine how much time the ride will take. The more vertical elevation gain on a piont to point the longer the ride time.

If you have a steep accent and a shallow decent wind may negate the downhill section as to make it seem flat or also up hill.

For touringcycling elevation gain will help plan how far you can travel on that day and the altitude indicator may help determine your kit.

Also for training or recovery ride. If you training ride is hilly or has cat one climb your recovery ride may want to be done on a flatter route.

Where i live there are few real hills. so i compensate by using the touring bike. Me, the bike and gear run about 330 lbs. Now add a 12 tent gear.
I did 83 miles packed, with out the tent, on a flat ride yesterday. I spent last night dealing with cramps as if i had ridden several long hills. With a head wind on my return of 10 to 15 mph my average was 7.6 on the return. The wind negated any advantage of the downhill.

Elevation gain will help to determine how you will prepare you diet for and before the ride.