Shadowing a builtin makes your code more difficult to read and maintain. It may also be a source of bugs as you can reference the builtin by mistake.
It is sometimes ok to shadow a builtin to improve the readability of a public API or to support multiple versions of a library. In these cases the value is higher than the maintainability cost. Just be careful when you do it.
It is not ok to shadow builtins with variables which are local to a function or method. These variables are not public and can be easily renamed, thus reducing the confusion and making the code less error-prone.
This rule raises an issue when the name of a local variable matches the name of a builtin.