DOC: Be explicit whether a view or copy is returned
#### Location of the documentation
For instance, 
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.drop.html 

#### Documentation problem

Sometimes the documentation is explicit that a copy is returned, e.g., https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.assign.html -> "Returns a new object ...", sometimes it is not or not explicitly stated, e.g., https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.drop.html -> "Drop specified labels from rows or columns."

#### Suggested fix for documentation

I wrongly assumed that pandas.DataFrame.drop returns a view because the first line of the docstring "Drop specified labels from rows or columns." suggests that, in my view. Later it is mentioned what happens if you set inplace = True. But you can only assume what happens if the default argument is used. Thus, the documentation is not clear w.r.t. this point and may be confusing to users, see #33438 or #30484. 

I would suggest that the documentation reads `"Drop specified labels from rows or columns and return a new object"' and/or "inplace : bool, default False. If False, return a copy. If True, do operation inplace and return None." This also applies to other methods that have the inplace parameter.

Since the use of inplace = True seems to be discouraged (#30484) it would also make sense to mention that in the documentation?
