If you already own compatible guitars, drums, or microphones, you don’t need to buy the full bundle. Guitar Hero and Rock Band games are backward compatible with older instruments, so you can purchase the game disc separately.
Bundles are aimed at new players who need both the game and an instrument. They’re a convenient all-in-one package, but they’re unnecessary if you’ve already invested in hardware.
Before buying, verify the specific game’s requirements—some newer features may not work with older hardware. Check the official product description for details.