While, the basic purpose of a presser foot is to hold the fabric in place while it is moving through the sewing machine, specialty feet can actually manipulate and control the fabric or embellishments to make certain applications easier. Many of these feet are universal snap-on feet, but there are some that need to be specifically matched to your machine, so when purchasing supplementary feet, read the specifications to ensure that the presser foot will work on your machine.
You may think it impractical to purchase specialized presser feet for sewing tasks that you may only do a few times a year, but after using, for example a binding foot, you may find yourself doing more sewing projects using that particular method because it is so much easier to do than before you purchased the presser foot.
In my case, it was a specific foot that caused me to purchase the sewing machine that I currently use. One day, I went into my local sewing machine store (Oh Cathey's how I miss you) and while waiting to pick up my serger from servicing, I started playing around on the display sewing machines and found this machine with a stitch in the ditch presser foot and fell in love with it. I was doing a lot of quilting at the time and I am not the best at stitching in the ditch when putting on bindings and those stitches that hopped the edge drove me crazy. Now, I use that stitch in the ditch presser foot constantly, and not just for ditch stitching, but also for edge stitching because I can adjust the position of my needle to sew a consistent distance from the seam edge. I would never go back to a machine without one now. Here's a quick video that shows you how the stitch in the ditch presser foot works:
There are many more specialized feet to discuss so be sure to check back to learn about the cording foot, the pin-tuck foot, the binding foot among others. There is even a button sewing machine presser foot that holds a button in place so you can sew it down! No more hand sewing buttons!