12” singles got a bad rap from the rock community. Rightly so in many cases where especially in the early years they’d just put the single tracks on them. Slowly labels realised that people deserved more than that and started to put unreleased and live tracks on.
For many years I wasn't interested, assuming it was primarily for extended mixes of dance tracks. I changed my view a few years ago and started judicially buying a few. One of the first was Ozzy Osbourne’s So Tired which was a 5-track EP with 3 live tracks which you couldn't get anywhere else.
And I discovered that many classic bands would put a live track or two on. Deep Purple rerecorded Hush as jam and put two unreleased live tracks onto a 12” in 1988. Like I say, you still have to be judicious because some didn’t take advantage of the format and just released the 7” 12” as the same.
I shouldn't really be telling you this, but usually a 12 is cheap because no one wants them. I usually pay no more than £3.00 and yet, in the case of So Tired, you get nearly half an hour of music.