Ha Ha, we always called it a ‘Jesus’ strap.
You can use it to pull yourself into the front of the saddle, thereby getting the correct feel of where you are supposed to be ie: NOT on the back of the saddle, but in the front, closer to the horses center of gravity. One handing it is, IMO, a bad idea, it lends itself to assymetry and who needs more of that?!!
Otherwise, proper use of the grab strap means that you are lucky enough to have managed to grab it before your horses bolts, bucks, rears, pulls some sort of stunt :lol: