Not Important.
Some functions, like search() work with plain strings or regex strings. Other functions, like match and contains work only with r, other functions like startswith work only with plain.
All the functionality is already there, but would it make sense to make these functions all orthogonal, so that they always work with either type of search string?
I have not fully thought this through. It may create other issues. Nevertheless, it would make it more conveniently easy to remember how to work on strings from an end programmer perspective.