I used one today with an embroidery needle (with a very large eye) to thread 4 thicknesses of thread through to sew on a button to my purse. It takes a lot less time which is needful for me as I am making several purses and I hate sewing on buttons.
My pics aren't the greatest, but maybe you can tell what I am doing. The button, loop, and straps are attached to the outside of the bag with the lining being the last step in the process. The loop for the button is a stretchy pony tail ring.
Source: My head
By Marty Dick from Knoxville, TN