It's mostly "useful" for how BEAM is deployed. Meaning brought up in the cargo trunk of a regular supply flight, as anything NASA for ISS currently is.
The current flight is only a conceptual test. BEAM will be mounted to ISS for two years and will during this time not be used in any way. The ISS crew has eight visits during those 24 months scheduled to check its structural integrity, and otherwise sensors will monitor integrity (air pressure), radiation load and temperature. After those two years it will be dumped into the atmosphere.
The downside of BEAM and other collapsible modules is that effectively they only provide empty space - while there's a need for that (part of the Japanese module is used like that - for storage, mostly), there's only so much you can really do with it. At best they'd provide mounting points for equipment later brought onboard by other flights for on-orbit assembly. At which point you can wonder whether it wouldn't be cheaper to package that into a standard module and launch on a dedicated flight.
What in my opinion collapsible modules similar to BEAM would mostly be interesting for would be a replacement of Progress for disposal purposes. Basically a pressurized trash bag that you can fill up for a few months and then either send into the atmosphere to burn up or set aside where it doesn't get in the way once it's full. Probably should be (slightly) smaller and (considerably) lighter than BEAM for that purpose.