Aiming by feel is like painting.. you don't need to know the exact size of an object that you're painting, because what you know and create just feels right. Of course, some paint much better than others.
Looking at bank shots, on some I have to take into consideration: speed, angle, spin transfer, collission spin.. or sometimes adjust speed and angle of hit to miss the double-kiss. I can't bust out a formula and plug in my estimated angles and speed, so I have to use feel. The same can be said with other shots.. if I'm cutting a ball in the side and want to spin off the short rail and side rail to bust up a cluster, how hard do I hit it and with how much spin? I don't tell myself that I'm hitting the CB to travel a potential 6 feet, with enough draw to pull back a foot and enough spin to come off the rail at a 45 degree angle.. I think to myself, "this feels about right to hit here and there with enough power for the break-out".