A friend of my mentioned that in his D&D 5th ed. game, a player was running from an enemy and wanted to shoot him in the leg to insure his own escape. D&D to my knowledge doesn't have any rules for hit locations, but my friend just ruled on the fly and the game continued. The reason that my friend mentioned this though was because he started to think of all the things that would have been needed to resolve that in GURPS.
That made me start thinking. In other games systems when a situation comes up where there isn't a rule to cover it, the GM rules on the fly using his or her best judgment. But GURPS has rules for just about everything. Because of this, people think that when a situation comes up that those rules cover, then those rules must be used. But the fact is, there is no reason why a GURPS GM can't just rule off the cuff.
GURPS is simple and GURPS is complex. How it plays in individual games is entirely up to the GM. Just because there is a rule to cover a specific situation, that rule doesn't need to be used if GM and players don't want it! Remember "And all the detail is optional – use it only when it makes the game more fun." (Basic Set p.8)
So, if hit locations add too much complexity to your games, don't use them. And if later a player wants to shoot a perusing enemy in the leg, rule on the fly. If you know all the modifiers off the top of your head (-2 or -BULK from Move and Attack, -2 for Leg, and Range penalty), then use that, if you'd need to look it up ... DON'T. Just make it up and keep playing.
I must admit that I've often found myself saying, "I know there is a rule for that" and started searching my books. This is a habit that I am still trying to break myself of. I'm starting to think that having to use an existing rule is almost as bad as forbidding an action when there isn't a rule that covers it. In both cases the GM can just guess at a modifier/target number/whatever, and let the play continue.
Rules should be there to help the GM and players, not get in the way. They should make interacting in the shared imagined world easier and create expected results from character actions. And whether a rule simply doesn't exist to cover a specific situation, or isn't know, or is being ignored, it doesn't matter. The play should be the same: the GM makes a call, the dice are rolled, and the game goes on.