Android Beam is one of the oldest pieces of Android that's still around after being introduced around Ice Cream Sandwich, offering a way to move files around between devices before NFC tags and contacts were common. But that now that NFC is implemented in tons of other ways, it's about time to put Android Beam to rest.
That's the plan from Google, at least, with the Android Beam API set to be deprecated in the near future. It's not going away immediately, but it won't be enabled by default in future versions of Android and OEMs will have to set it up for devices just like they currently do with NFC. That's bad news for Android Beam as a whole, as many manufacturers will likely just let it fall by the wayside. It's not used particularly often, so there's not much of a reason to keep it going.
Honestly, though, I don't think this is anything to really worry about for most users. Transferring files is incredibly easy these days, whether that's using LTE for email, cloud storage, or messaging platforms, or things like Google's own Files Go's offline file transfer feature. There are a ton of ways to do things that are better and more intuitive than Android Beam, so this is really just more of a formality than anything else.
source: XDA Developers
