If you play alot of guitar or other instrument or sing etc, you can use your joints repeatedly in the same way, and this puts the same stresses on the same joints and muscles. It also can be a bad posture sitting or standing in the same way for long periods (whilst being focused on some technique or performance). It's important to stretch out your finger joints and wrists. And to just "shake it out", to get the blood circulating throughout your whole body, and to re-invigorate your full nervous system with blood that might not have been getting it. Or something like that. Basically, it's just feels good to shake your whole body out every day, just shake your limbs out and wring your fingers, and wrists a bit, and your ankles, rotate them, and rotate your neck around, roll your eyes around your head NEWS, open and close your jaw fully. Make gibberish sounds, cry like a baby, just let your "lizard" system take over, and let that "Animal" part of your physiology do what it needs to do. Because you can go for long periods at work or whatever, where you are seated in the same way, and your body can get very stiff and cramped up. Doing a little dance and some hula hooping is also nice, just because it gets your body moving, into a rhythm. And when playing or peforming, it just makes things that much more fun and into it if you really move your limbs and get a groove.