[satyrnein]

In my experience, people don't start out with the goal of loading indicators on buttons. It's usually the mistaken idea that avoiding a page reload will make the action faster. Instead, you now have a slow Ajax call, and the button appears broken, so now it needs a loading indicator.

[chrisco255]

"a slow AJAX call"? What is even meant by that. Async JS is not slow. It's only limited by the user's connection speed and amount of data to be transferred and server response speed. This is a few dozen milliseconds but can be optimized down to sub 10 ms (the server and latency is the bottleneck not JS). A full page reload will of course take longer because instead of one tiny JSON object you have to send the full HTML back down the wire, and the screen also completely repaints and sets up a whole new DOM structure in memory for the same components.

[satyrnein]

I was referring to the server being the bottleneck, as you mention.