DIS: Should the keyword use_nullable_dtypes use nullable dtypes in the absence of nulls
Currently the keyword ``use_nullable_dtypes``(only implemented for read_parquet now) will use nullable dtypes for columns even when that column does not have nulls.

Should this behavior change?

xref discussion https://github.com/pandas-dev/pandas/pull/40687#issuecomment-833447019 https://github.com/pandas-dev/pandas/issues/42588#issuecomment-894981214 
https://github.com/pandas-dev/pandas/issues/42588#issuecomment-882773411

(Note that always using nullable dtypes always(the current behavior) is a choice made on our end https://github.com/pandas-dev/pandas/blob/master/pandas/io/parquet.py#L215-L227 not by the pyarrow engine)

cc @pandas-dev/pandas-core