Less cable installation. Put it on a pole pointed toward the tower and you're done. It'd be nice in the US where the corporate cartels like Comcast/Charter/Verizon can't as easily blockade access to internet by manipulating control over utility poles through bribery of local and state officials.

nice laser link, would be a real shame if we built a tower in between...

I'm thinking that it'd be cheap enough to route the beam around a tower that this would be cost prohibitive, but it made me laugh.

The decreased propagation time through air vs glass likely wouldn't yield latency improvement in relevant orders of magnitude. The primary benefit is cost reduction. Erecting a few towers with optical relays over high points in terrain would be cheaper overall to install & maintain than either aerial or trenched fiber. If a 3rd party builds something in your way, just relocate the tower whose line of sight becomes obscured (on the assumption tower sites are solar-powered and self-standing).

Potentially cost of the fiber optic cable and the installation of it.

Also no idea in India but in the US a lot of times although their are existing power poles internet providers can't necessarily get permission to string their fiber on them. Same problem can happen with existing in ground pipes. And any trenching or installing new poles becomes very expense.

The slowdown of fiber vs vacuum is about one third. A 33% reduction in latency is fairly significant for some applications. I've heard of financial trading firms using microwave relay towers for this reason.

The other issue is "long fat pipes." TCP is better tuned for it on machines now than it used to be but when you go over a long distance, the latency can decrease the usable bandwidth significantly. Of course, this seems to be more focused on last mile rather than back-haul. There are very few applications where a several nanosecond latency decrease matters.

Cables are cheap, but require maintenance.

An alternative way to imagine networking an area is running fiber into the area then having a mesh network assemble itself building to building in town/city whatever. This has the added advantage of greatly reducing the power costs of the overall network for local communications.

The labor cost, materials cost, maintenance cost, and right of way / easement cost in laying cables is a huge barrier both cost, time, and pain in the ass wise.