It’s something a session guitarist I once took a lesson with said to me along with thoughts on posture; I wish I’d been told it when I was much younger. In all likelihood, your fingers are too far from the frets when they aren’t being used – dangling out in the ether while another finger is busy doing the fretting.
This is bad for two reasons: firstly, you expend extra energy every time you bring a finger down to fret a note, and (as a result) secondly, you have less control over what you’re doing. I see this habit all the time particularly with more technical metal guitarists and bassists who have focused on learning scales and executing things fast, thus letting their slow and steady fundamentals fall by the wayside. The speed that I usually find in young metal bands is a kind of false speed – like a low-res rendering of an image by a computer that has sort-of-fast Internet. All the information of the image may be there, but the fine-grain detail has been lost by skirting around the hard work it takes to render each pixel individually.
For some music, this can work to a nice effect (sloppy grindcore), while in others, it can sound pretty tough (sloppy tech death). It’s a strange thing though – take for example that Cannibal Corpse song “Frantic Disembowelment,” the instrumental version of which is a kind of holy grail for tech players. The song is great and the sort of flailing nature of the playing does work for it, but there’s a kind of tense, static-y feeling that comes out of the amount of extraneous movement the non-fretting fingers are doing.
The other interesting thing is that I don’t think this stuff applies neatly to drummers. It’s the opposite case actually – if a drummer’s arms and body are too close to the point of contact, their playing sounds tight and uncomfortable. I think drummers need to aim for more of a halfway point, in which the point of contact between drum head and stick head is close, while the arms are looser and more able to respond to the energy coming from the shoulders and spine. See for example Billy Rymer of Dillinger Escape Plan:
A metaphor that a piano player told me recently was that you should imagine that you’re an Olympic figure skater; your wrist is your leg, and your fingers are the ice skates. Your aim should be to glide along the fretboard. You can’t execute a beautiful triple axle if your feet are flailing around – you have to be gliding loosely, but with a close control over your footwork on the ice. Your goal should be for all of your fingers (including your pinky and ring finger, the weaker fingers) to naturally find their foothold on the fretboard.
So practice a simple scale (say the major scale) slowly, watching each finger closely as you fret the next note. All four of your fingers should be close to the fretboard, so that you’re not stomping on a fret so much as you’re locking into it like Matthew McConaughey’s space ship in Interstellar. It takes time to develop control to play fast this way, but ultimately you’ll find music is much more rewarding and natural when you’re not struggling to play your riffs.