Ferrites are often used to filter incoming power. You may be worried about noise coming in from outside your board. Oftentimes EMI is introduced to PCBs through their initial power source. Ferrite beads are great for filtering out that kind of high frequency noise.

Why do we use ferrite beads?

Ferrite beads and cores are used in equipment design to suppress and dissipate high frequency noise levels caused by electromagnetic devices. Ferrite components are used to attenuate EMI and can be extremely effective. Of course, using properly installed and grounded shielded cables helps suppress EMIs.

Are ferrite beads necessary?

Why the beads are useless. Ferrite beads are designed to block conducted interference at radio frequencies. Radio frequencies are not what the typical analog SDIY circuit needs to be protected from! ... There just aren't any ferrite materials that run in the lossy mode at audio frequencies.