Why use straps...

Probably considered more of a harness that simple straps, but kind of a good idea anyway. The one's on the market just encased the elbows, or just the one's I have seen in person. If it stays in position, than great.

Art Jones build his whole concept of the Nautilus pullover machine (lesser extent, his shoulder machine) with the elbows leading the motion of the exercise. Which in return took the weaker link of the arms and grip out of play, with the better leverage/strength of the elbows having the most responsibility of moving very heavy resistance.In other words, the lats/back can be worked to their fuller potential. One of the reasons that the Nautilus pullover machine is so superior a tool for building muscle mass. Most regular exercises (BB/DB/Chins) will depend a lot on the position of the elbows.

Anyone with experience with football, or even basketball, will understand the potential power of the elbows in close contact with another player. When applied correctly, you can move another player in just about any direction you want. Hitting another player, with the elbow, can have a powerful and damaging affected (just don't get caught). Martial Arts, and other fighting arts, including boxing, depend on the elbows for counter attacks and blocks. Bar bouncer's (the more skilled one's) know the importance of using elbows at selected times. Good Luck.