The only place I think it is useful is for Android. It can take a while before the app gets to the point where it is executing code (written by the developer, not TGC). Getting the splash screen up shows that something is happening.
On my faster Android devices, there is still a black screen for about two seconds before the AGKSplash.png displays, and then that is up for 3 to 4 seconds before the 'custom' splash displays.
On my slower ones it is about 4 and about 7 seconds.
On iOS, you are required do the minimum Default files and they display instantly. And on Windows, the core AppGameKit loads lightening fast.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master