I'm copy/pasting what user DannyBee (his about on HN: "I'm an open source lawyer who hacks on compilers" via
https://news.ycombinator.com/user?id=DannyBee ) has said here
https://news.ycombinator.com/item?id=9113324 - he's replying to something another user said -
"Facebook is granting you additional rights on top of the BSD license. In the worst case, where you do something that causes the patent rights to be revoked, you're still left with the same rights you have under the BSD license. This is unambiguously safer to use than if they had released it under a vanilla BSD license. As for why Facebook did this, they're most likely trying to give away additional rights while still maintaining the ability to use these patents defensively, in the event someone sues them for infringing a different patent."
This is 100% totally and completely wrong :)
The BSD license normally includes an implied patent license.
It says " Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met .. "
This grants an implied patent license to the patents necessary to actually do this, as long as you meet the restrictions.
This is actually well settled law. You don't get to give people stuff unrestricted, and say "you can use this for free", and then say "just kidding, what i meant was, you can use this for free as long as you pay me for the patents"
However, when you do what facebook has done, and give an explicit license, you have overwritten the terms of that implied license, and you get no implied license.
So it is not only "not unambiguously safer", you are not "left with the same rights you had under the bsd license if it is revoked".
This is because if you revoke the explicit grant, you get nothing in terms of patents. But the implicit grant is not revokable unless you violate the copyright license.
So sorry, but this is not "better than the default" and does not in fact, help you.