My philosophy is this:

Playing an instrument is difficult. Why make it more difficult than it needs to be? You're a machine, moving your body parts from one place to another in order to transfer energy to your instrument and make sound. If you can make the same sound with less energy, then why not do that?

Always take a look at your hands / arms / neck / back / face and determine whether they are in an inefficient position or wasting energy. You can figure this out by making a video of yourself and seeing what you do. Try to make your body into a machine where each part doesn't strain too much or have to travel too far. You can learn this concept from martial arts, too.

If you were to work in construction, hammering nails all day, you wouldn't be raising the hammer high in the air above your head with both fists. Many of the strokes would miss, and you'd be putting the nails in at the wrong angle, bending them, denting the wood. You wouldn't use too weak of a stroke, either, because then it would take you 10 minutes to tap tap tap one nail into the wood.

You want to find that most efficient usage of energy.

-Carl.