This is a great method for nailing left hand events.
A left hand event can be anything. It could be a big shift or an awkward jump or something that requires a change of hand position. A LH event is just something that gives you trouble.
The name pretty much explains it all. Play something, STOP, move to the next thing, GO.
Let’s take a look at the first measure of Carcassi’s Etude no. 2, Op. 60.
There’s a shift and and a chord change. You’d play the first two beats. STOP. Then move to the next chord shape, and hover just touching the strings. Then GO, pressing the fingers down and beginning to play at the same time. After practicing this way and getting the movement patterns ingrained, the development is very similar. Play the first two beats. STOP. Consider carefully what your hand must do to get to the next chord cleanly, but don’t move. GO, shifting, placing the fingers and beginning to play again at the same time.
The time in between events gives you time to think. Strive to for the perfect hand position and no biffed notes or mistakes on the second two beats. In short, this method allows the left hand events to be practiced perfectly. After practicing like this, shifts and chord changes and other events giving you trouble will often recede into the background. A good measuring stick of effectiveness (and whether or not it’s time to move on from stop/go) is comfort. When we deal with a difficult left hand event, it feels hard. It feels like we’re floating on the edge of disaster at concert tempo–ready to slip up at any time. After practicing stop/go that comfort level increases, the section should no longer feel on the edge.