Generally speaking, CmdletBinding is what makes a function into an Advanced function. Putting it at the top of a script makes the script an “advanced” script. Functions and scripts are much the same, where the script file name is equivalent to the function name and the script content is equivalent to the scriptblock section of a function.
CmdletBinding attributes give you control over function capabilities, such as adding Confirm and WhatIf support (via SupportsShouldProcess), Disable parameters positional binding, and so on.