If you forget what you were doing 5 seconds into doing it, you may want to get your dementia diagnosed...
Splash screens are useful when a program needs a lengthy time to start up, so the user is aware that the application is responding and to prevent them from launching the application a second time during load. It's perfectly acceptable for a program like Hammer to have a splash screen because it does some pretty expensive WAD file scans when it launches. Now that CPUs are much faster than they were 15 years ago the WADs load pretty much instantly, but back in 1998 that could take a few seconds to complete. Sledge loads WADs when a map is opened rather than when the application is loaded as it allows WADs to be added without needing to restart the app.
As for the 'features' in this Hammer mod...they're not. There's some UI tweaks and FGD modifications, but nothing significant that could be called a 'feature'. It doesn't really apply to Sledge because these are specific to Hammer. As for the FGD mods, they should work in Sledge by default (once model rendering is implemented).