Another situation where three fingers if preferable is with fast, simple lines. Line below is meant to be played in sextuplets, not sixteenths. As you can see, the notes are grouped into fours and a seven. These are not divisable by three, but you should still use three fingers. Since there is a pause between each group, we can cheat a bit and not keep the order of plucking. So we will play each group starting with finger 1 regardless of where the last group ends. It is completely acceptable to do this when their is a pause in the line. So we will play this line like so: 1,2,3,1 ---- 1,2,3,1,2,3,1 -- 1,2,3,1 -- 1,2,3,1 ---- 1,2,3,1,2,3,1 -- 1,2,3,1. Try playing that with two fingers and it won't be easy.