These little rubber bands are fantastic for use on your practice chanter reeds. Double-wrapping them over the blades of your reed will make the reed easier, softer, and higher pitched. These bands give an added range of adjustability to your practice chanter reeds. Moving the band up towards the tips will make the reed easier, and moving it down will inversely make it harder.
You can also use them in the same way on your cane bagpipe reeds. They will have a similar effect on pitch and strength and are a great way to help you break in a tougher reed without shaving any cane off. It is recommended to use them above the halfway point on any reed. Moving them on or below the sound box will make the reed chirp and squeal. These should be removed from a cane reed after the initial break-in period.
Take a look at our blog about a "Checklist for a Comfortable Bagpipe": https://www.jhiggins.net/blog/checklist-for-a-comfortable-bagpipe/