I use clips when sewing handbags, purses etc, also when stitching some leather or faux leather trim on jackets etc. I started with the size in the above photo, then bought some longer ones which also open wider and therefore great for quilts, jackets etc.
The longer ones were great when I made a quilted patchwork jacket last year, however I still use pins at times too, just depends on what I'm sewing.
To someone asking if clothes pegs could be used...I tried these prior to buying the clips and while they work at times, the clips are a better design for machine sewing. They are flat on the base, so the item you are sewing will sit flat on the machine bed or free arm. They are also 1cm wide and the mouth area is 1cm deep, so you've got an instant measure guide as well.
A tip for anyone interested in buying the longer ones...I bought red for the small and dark green for the long ones and while I keep them in separate small baskets, it's easy to see at a glance which size you are using and also where they are located. I just bought the chinese ones on eBay, much cheaper than the branded ones in sewing or quilting shops.
A great little invention, I have NO affiliation just use them quite often, but for me, they will never replace pins. Hope this helps someone?