That actually looks like an appropriate use, as it is retrieving, writing, or appending the file contents of a remote file via FTP transport. I was at a conference probably 2 years ago where the person was using TCP/IP communication to interact with a field device for scientific research.
In short, he was given an API detailing the stream headers, commands, etc that you can send over a specified port to the device and it would respond back with the information you asked for. I don't quite recall the language he was using (I think it may have been .NET with a C++ satelite DLL for some of the transport routines), but it was interesting nonetheless.
The only problem is I don't see PHP being the language I'd choose for these operations. Most of the time you want to do relays or verbose communication in these situations where you need threading or stacks of some sort. PHP just doesn't seem well vetted for the scenario (but again, I always state, choose the right language for the job, don't fit the job into a language).
Where PHP may be able to use this cleverly is back when IP cameras were not web accessible already (meaning they ran their own built in program) and you had to interact with them via TCP/IP to get the picture/footage and the communication would be fairly short, authenticate me, thanks, now give me the latest image! streams always gave me the feeling of having to be very much involved in the networking side of IT and I despise that side (I'm just not cut out for it!), so I tend to stay away from it.
What could be an interesting challenge, is to see which performs better:
Or using stream_get_contents after verifying the tcp transport is available for use.
Hmm, I may have to add that to my to do list...