As a long time traditional Japanese jujutsu technician. Who knows how to kick and punch, who has been in scraps that where not pretty, I have thought allot about this. Here is what I have come to in terms of self defense:
Joint locks and Joint brakes
Joint Locks: for compliance. I have a drunk and I need a hold for compliance reasons. He is drunk easy to get the lock. If he isn't drunk, if he is aware of the lock coming on, is strong, is moving aggressively, a strike is necessary first before the lock. No strike need if he errors, i.e. a very lousy fighter.
Joint Locks for non-compliant situations: An attacker grabs by arm to hold it, or grabs hair. A strike, if possible, followed by the technique is preferred. The other guy errors as a result of a lousy fighter, then a technique is applied. Again a strike is preferred to soften up the attacker to apply the Joint technique.
Joint brakes: other guy has a weapon and intent on hurting or killing you. You must control the weapon. The above applies. You must strike or he must error, providing an opportunity to apply the break.
Personal insight:
Personally Joint locks are not the primary technique I would use. Breaks over locks primarily. Because the opportunity is specific and exacting to apply an effective lock or brake. Because it requires skill, good timing, and often a distraction such as a strike. My experience and training tells me to punch and kick first then apply the jujutsu if necessary. But in rare cases, if the window is there, you lead in with a joint technique. You can fight all your life and maybe use one or two techniques of joint locks or brakes as described above.
A good , and I stress good not lightly, Hapkido school isn't a bad thing.