· The capo obstructs your playing

When you play certain things on the frets closest to the capo, the capo will interfere with your hand. The bar of the capo is wider than the fretboard and most capos have yokes, screws or handles on the back of the instrument neck. So, naturally, you place the capo away from your hand, behind the fret. However this will cause:

· Tuning problems

If the capo is placed away from the fret, it will bend the strings. The bass strings will be bent more than the treble strings, because they are thicker. They have a thin steel core, so they bend as easy as the treble strings. The further away from the fret the capo is placed, the easier the strings are bent and the harder the capo have to be tightened, in order to prevent the strings from buzzing against the fret. All strings will be pitched too high, and the bass strings will be more out of tune than the treble strings. The strings are actually fretted twice - by your fingers and by the capo.
    The only way you can avoid tuning problems, is to line up the edge of the capo as close to the top of the fret as you can get it!   In this position the fret itself and the stiffness of the strings will prevent the strings from being pressed down too far. One extra second to line up the capo carefully will save you (and the audience) from a lot of retuning. When the applause stops, you'll be ready to kick off the next song. But of course! This brings us right back to where we started - the capo will interfere with your hand...

· Strings are pulled sideways

Every capo goes into a certain position of equilibrium when you attach it. If you don't hold it in that position, it will go there anyway. The strings are often pulled sideways and you have to make a new attempt to fasten the capo. Sometimes the strings are not pulled aside at once - the capo might change its position when you start to play and the strings vibrate. For most capos attached from the side, the position of equilibrium depends upon the thickness of the instrument neck.
    This problem increases as you become aware of the tuning problems. When you place the capo close to the top of the fret, you also want the capo sticking out on the treble side as little as possible to minimize the interference with your hand. As a consequence you try to force the capo out of its position of equilibrium.