I love locks (they're great with bagels, but that's another kettle of fish).
Seriously though...
Both of the arts that I practice, Modern Arnis and Aikido, use them extensively.
I'd be interested to hear how people here who train in locks train in getting to the locks. Different arts have different approaches.
I first learned joint locks in a Modern Arnis class with a heavy emphasis on the Small Circle influence. Thus, I not only focused on the minutae of lock mechanics, I also worked on applying locks from various empty hand and stick exchanges. There are plenty of Arnisadors here who know how much fun it is to try to apply a lock while doing de Cadena trapping hands. I feel that this training has caused me to focus on "stickiness" and the anatomy of locks, so in training I often find a lock when I "feel" it, without having to look for it. If this makes sense.
Understanding joints, both objectively and subjectively, also helps with understanding joint locks. I spend a lot of idle time just stretching my joints, feeling their limits and thinking of what motions produce pain, immobilization, etc.
When I started Aikido after several years of Arnis, I was able to make most of the joint techniques "work" right away, even if I hadn't learned them in exactly the same form before, because of the training I described above.
Stan