Why is this an issue?

There’s no point in forcing the overhead of a method call for a method that always returns the same constant value. Even worse, the fact that a method call must be made will likely mislead developers who call the method thinking that something more is done. Declare a constant instead.

This rule raises an issue if on methods that contain only one statement: the return of a constant value.

Noncompliant code example

int GetBestNumber()
{
  return 12;  // Noncompliant
}

Compliant solution

const int BestNumber = 12;

or

static readonly int BestNumber = 12;