Last minute gate changes or departure time changes can be challenging. Many airports have terminals that are miles apart. That doesn't necessarily mean you need a fancy app, but things like SMS notices for that sort of thing are very handy.

Google does a fairly good job at aggregating the info so you can search for flight status, but you have to actively poll for it.

For that reason, many people have lots of individual airline apps, or lots of individual sign ups for notices.

Similar for keeping your air, car, and hotel reservation details somewhat "together".