Is it a good idea to pick strings without anchoring your right hand?
The right hand just stays hanging in the air while picking.Does it decrease accuracy ?
In most of my students, yes! Floating around can hardly do anything except decrease accuracy. In initial stages at least, resting the hand just behind the bridge will anchor it sufficiently to move the picking onto the next string. And for the next few years too. And for palm-muting, move it across a little. Some find it beneficial to rest pinky on the guitar body, just under the top string.
Anchoring is a pretty bad habit to develop. If you are serious about developing exceptional technique then invest the time in a floating right hand. It is more difficult and will take a lot of practice but in the end you will develop greater accuracy.
Anchoring does two things that will come back to bite you. The first is that guitarists that anchor will more likely than not play in one area of the instrument or one a small group of strings. The second is that in many cases when playing fast an anchored right hand can actually cause you to push away from the guitar making the pick miss notes (this is very sloppy and inaccurate).
There are exceptions to every rule. For example Mike Batio, Yngwie, and Wes Montgomery all anchor, but they have specific ways to do it that work for them. Yngwie does not always anchor, and Wes is using his thumb, pushing in as he plays. So the general comments do not apply. People have written text books analyzing Yngwie's technique, if you like that sort of thing you can look it up. But there are many great shredder who do not anchor in this manner and still fly. You do need to develop a haptic connection to the instrument and for beginners it is tempting to anchor to help them "feel" where they are on the guitar. But the truth is you don't need this for accuracy. What you need is lots of practice. In finger style classical guitar your connection is the forearm touching the edge of the body, no anchoring of the fingers on the top. And some players lift the arm when playing across all six strings (essentially floating the arm).
If you look at Frank Gambale's technique he rarely (never as far as I can see) anchors the fingers on the top but he keeps the palm of his picking hand very close to the strings, to the point where he probably touches them. When Eddie van Hallen tremolo picks he floats his picking hand in the air and he is extremely accurate.
For me personally, anchoring limits mobility and speed. With practice a floating hand is just as accurate as an anchored hand (in my experience more so) and I teach my students a floating right hand style.
Interesting question. I play with a pick and most of the time I anchor my picking hand when I'm improvising lead parts. However it might be interesting to learn to play un anchored which would allow me to play away from the bridge where I might find other tonal characteristics on the guitar. If I were to learn to do this, I don't think I'd give up anchored picking completely, but it might be nice to have those alternative skills on occasion.
What I do is to keep my pinky on the guitar's scratching board (or simply on the body if your guitar doesn't have one) while playing lead.
Its a good practice as it increases accuracy while playing lead. However, if your're playing power and barres chords, wherein you've barred 4-6 strings, you can remove your pinky. The same goes for open chords.
But, for short chords (short forms of full barred chords), you can keep you right hand anchored.