Use this trick if you want to make adjustments, or try to perform more than just the routine maintenance of oiling and lint removal where you have to remove and reinstall very small screws or very small parts. I know from experience that if you drop one of these bits, it will launch itself off of the work surface and disappear forever in your carpet, or if it hits a hard surface floor, it will scoot to a place where it will never be seen again. This happens at near light speed, and while you think you know where it went, you will never find it.
A sure fire way to prevent this from happening is to place the machine on a bath towel or other thick pile fabric. The color is your choice but white works well for me. The thick pile will prevent the part from bouncing and it will sit right where you dropped it.