The concept is fairly simple: For a set price, travelers flying on United are entitled to one or two checked bags for the entire year, starting at $349. It's an appealing option, now that basic economy has become the de facto standard, especially for couples or groups that love traveling together.
Subscribing doesn't necessarily allow for a carry-on bag on basic economy fares, but it does allow for a checked bag, making for a less ghetto flying experience. Maybe that's worth it in of itself.
Perhaps, though, the best value is for families that don't want to juggle kids and luggage all at once. It would take a family of four 3.2 trips to Grandma's house to break even. Bachelorettes, anyone?
Pricing varies depending on the number of travelers, the number of bags checked and region. There doesn't seem to be real use for most international travelers, though, since most airlines still allow checked bags on international itineraries (for the time being).
If not, there's always basic economy à la carte.
Cost of a domestic baggage subscription.
How long it would take to break even (in roundtrips).