Closes #61057

• This PR adds a docstring note about the inference behavior of apply with result_type='expand' when function returns NaN-like values, as discussed in issue BUG: Inconsistent behaviour of apply with result_type='expand' for functions that can return NaN type values #61057.
• Added docstring to distinguish behavior for 'apply' method.

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Personally I think we should deprecate that parameter. Since I guess you're using it, do you mind sharing an example of how you are using it?

You'll have to remove the blank lines for the PR. Also, did you check if what you are detailing is only affected by expand, or also by reduce?