I use them because the shop I got the rims from was out of tape at the time that I purchased them, so he gave me a good deal.

After building the wheel, and spending 10 minutes popping them into place I thought they were stupid.

..however, later on, when my chain ate three of my spokes, and I was able to remove those 3 plugs to hold the nipple steady during the replacement, I didn't mind them so much.