There's a ton of useful applications for stuff like this. You wouldn't use it for access in heavily populated areas but there's plenty of usefulness in disaster areas, remote areas and military application. Not every technological development is about getting Netflix to your home faster.
A drone that can fly above a hurricane could be available immediately after any natural disaster except for a solar flare. That could make relief efforts a lot easier, by allowing organizations to coordinate without needing satellite equipment or relying on possibly damaged/destroyed infrastructure.
In sparsely populated areas, consumer internet access could be provided at a much lower cost than laying down fiber across long distances for a very small number of users that will be obsolete by the time it is finished being laid. By default these areas will have mobile access as an added bonus.
In terms of defense, a robust network that can easily recover from an attack is highly valuable. With drones instead of fixed nodes you can very cheaply introduce redundancy into the system. Even if you had to launch a new drone, it's a lot faster than sending a guy out in a truck to find and fix a broken line. This gives you a potentially uninterruptible network.