i agree with what yablanowitz said, maybe i can add some too...
when you think about it traditionally, the sheepsfoot is great for wood carving and as a mariners blade, no point to puncture\hurt yourself, no curve in the blade equals no slipping like a clip point can, and the cutting edge is straight making it easy to sharpen. Coping blade is most useful for wood carving (thin blade gets into places good) and as a marking blade for lines instead of a pencil, it props up against the ruler for a perfect line. Spear point is just a general all around knife, very strong design. And the pen blade was traditionally used to sharpen quills (feathers) to dip in ink and write with, the name stuck - pen blade.