When I was young, my father often talked about research the Soviets did with weightlifters using a dynometer which showed a high correlation between grip strength and a lifter's success or failure on the competition platform. Lifters who had poor grip strength prior to an snatch or clean and jerk attempt would very likely miss their attempts and if their grip was strong, they were likely be successful.
Surprising? No. A good grip can be an indicator of many things, including excitability and proper rest - it only makes sense that a competitor, sufficiently rested and psyched up will perform well on a grip strength test and likewise perform well on the platform. However, it can point the way to other things as well, such as the importance of having a strong grip.
Jedd Johnson of the Diesel Crew said on the Dr. Squat message boards (many years ago now) something to the effect of "a strong grip = a strong EVERYTHING". I don't know if that's true all the time, but it is certainly true that a weak grip can ruin all kinds of performances that would otherwise be very strong. For example, in the fighting arts, such as wrestling, judo, and jujutsu, NO ONE becomes good with a weak grip and neck. Have you ever heard of a weak-wristed striker? And a strong deadlift does not exist without a grip to match the posterior chain.
A point light figure like in the picture below, immediately highlights many structures that are regularly neglected in training, namely the neck, the wrist and hands, the hips, and the ankles and feet.
Any injury is bad, of course, and everything is interconnected, but we can work around some injured areas more easily than others. All of the areas highlighted above, when injured, can completely incapacitate us. A bad shoulder or hamstring and we can somehow manage, but injure an ankle or dominant hand and we are in a world of hurt.
So what? The bottom line is that if the only exercise a trainee does in the gym for the lower body is set after set of badly performed barbell back squats, then we're leaving a lot to be desired. Power generated from "the core" will not be expressed if dampened by weak and soft end points. The inclusion of exercises that stress and strengthen the extremities (at least on an occasional basis) are an absolute necessity for any program that claims to be "functional". This doesn't mean an additional half dozen isolation exercises - hill sprints and heavier sandbag work will cover most things. But, they need to be included.