Well, in order to find a use for the assembled PCB you have to figure out what it is, if you get a useless one, then you scrap it for parts.
I'd say about 80% of what's inside is useful, it's just finding something to use it for.
Some of the parts are impossible to identify, so they can be scrapped or tossed, like I got 4 little discs with a bunch of holes in them, they're not connected with copper, or anything like that, and there's an odd number of holes, so it's obviously not for an LED block, possibly a buzzer cover, I dunno.
I also got this small package of tiny SMD thingys, I can't figure out what they are, the bag they're in just says sample, and nothing else, so I dunno, I also got what looks like an electroluminescent square, but I can't tell, it's got 2 leads, and is in a plastic case, so it's either that or a clear solar panel (HAH! yeah right...)
I also found 1 broken circuit, which I tossed, and a few little things that almost look like a part of a robotic leg or something.
And I got a few other things I'll never have any use for, like a high current pot resistor that's only rated at 500 Ohms, it's HUGE!!! like 2" in diameter, and 3" long.
I also got some other stuff I can't identify yet, most of the unidentifiable stuff is surface mount, since I've never worked with it. Other than that most of it is useful, but then again as long as you can figure out what the hell it is, everything's useful.