What's in the boxed set that is an independent rule or item?
...eh? What do you mean?
What do you need from the boxed set that isn't available elsewhere?
Ooooooh.
For starters, just using it for it's intended purpose of teaching new players.
I love Shadowrun and its' setting, and I'd like to be able to be able to show the game off to as many of my friends and possible to get into the game. And I want to take all the tools I need to do so. Moreso since for whatever reason, Shadowrun doesn't really have much of a presence in the tabletop gaming scene here in Los Angeles.
(come to think of it: tabletop gaming doesn't have much of a presence at all here in Southern California when it comes to official events and cons. There's the token D&D and Pathfinder stuff at SDCC, but that's about it)
Well, the condensed rulebook would be nice to have to strip the rules down to their bare basics, but at a more advanced level then just the QSR. Having a series of adventures that are meant to be very basic kind of runs that ease new players into what Shadowrun is typically like. We even have the added bonus of individual missions for a single character to teach them the basics of how to play their archetypes. Also, spell and gear cards, official SR dice, and maps are also nice.
Now, I'll concede that the state that the Box Set was released in Digital form is far from perfect. As it was, there were some areas where you needed the core SR5 book to clarify on some things due to critical sections being missing. It's not completely broken and useless, but it could be way, WAY better.
As for the "Why can't you make this stuff yourself?" Thing is, is that the whole point of these kind of aids is to cut down on the amount of work that the GM has to make. I have very little time as is to properly chart every relevant table is in the core book, or making a my own gear cards. To have something already prepared for me before hand, and to give me one less thing to worry about when preparing for a session, I have a hard time seeing how that could ever be a bad thing.
(unless if the game aids don't work as intended, which is a different matter entirely)