Pocket is Firefox trying not to fall behind on features.

And presumably from Mozilla's perspective, if it has some sponsored content giving them some non-Google income, so much the better.

There are services, of which Pocket is not the only one, that save you personal hard copies of content so you can have it available offline and keep things even if they're gone. Like a personal Wayback Machine. It's a very sensible thing to integrate into a browser in my opinion, although a lot of the Firefox fanbase, being idiots in love with the idea of FOSS donationware, are hostile to. I used to be one of those idiots.