Lately, I found out that Application Launcher also features all the functionality I use from KRunner.
In my particular experience, Application Launcher is snappier at first launch and also returns results rather quickly. For me, this begs an obvious question.
What's the use case for using KRunner over the Application Launcher?
So far I've noticed that pressing Enter on the Calculator results makes the entry be copied on KRunner, but this does not happen for the Application Launcher. I'm certain there must be something else to it, otherwise people would not be using it (even I found myself using it from time to time, but could not understand why).
Clearly, KRunner exists so that if Plasma crashes, I can run
plasmashell --replacein there. 🙃Alright, a somewhat more serious response: It gives people flexibility in how they can use their system. For example, the Application Launcher requires having widget for it on your panel. It requires having a panel.
Personally, I also just like KRunner, because it doesn't take me out of my workflow so much. The Application Launcher feels like I'm now doing the separate task of launching an application, with how it slaps that flyout into your face, covering your windows underneath. KRunner on the other hand feels like I'm merely adding another window.
In general, though, you might not find massively convincing reasons to have it, because why not? They use the same backend code. The tiny bit of UI to display KRunner, that doesn't cause much maintenance. Even if it did cause much maintenance, it's not like the volunteers working on that are going to work on something else instead.