Back in the day splash screens were needed to give you something to look at while things loaded. So you could be sure the program started when you clicked it, and you don't keep clicking because you weren't sure, then have multiple instances starting. It's a well established UI/UX principle that you should immediately give the user feedback when they interact with something. Don't just sit there working in the background and leave them hanging.
These days, it's more about one word: Branding. It's the software equivalent of a billboard.
Hopefully, they'll have the option to disable it.
I can assure you, the 3-5 seconds (or more depending on your potato) it takes kicad to start up on Windows is not because of branding but because of how Windows file system caching works. The first start (after a Windows restart) will always be slow and it's not even a KiCad controllable thing. The subsequent restarts are always instant due to said file system cache. This extends to many programs throughout the history of Windows and Microsoft has never really improved it.
Conversely, macOS and Linux apps start near instantly because there's no caching layer operating in the same way as Windows does it. Coincidentally, the splash screen currently appears and disappears in less than a blink of the eye on those platforms
![Tongue :P](https://www.eevblog.com/forum/Smileys/default/tongue.gif)
You can even see this behavior on Windows when causing a KiCad footprint library load, the first time on Windows, depending on your PC can be a slog taking tens of seconds. Every subsequent restart is really fast and that's not due to anything KiCad is doing but that silly disk caching layer.
tl;dr, the splash screen is adding absolutely zero overhead, it does not have a magic delay timer. It is loaded immediately on launch and closes the first chance loading is complete.
Maybe we'll pencil in "disabling the splash screen" as a feature in v10.