What is the difference between a woman wearing the niqab with the intention of it being obligatory and wearing it with the intention of it being supererogatory, and what are the implications of that?

Scholars have differed regarding the ruling on a woman covering her face and hands in front of non-mahram men. For a woman who wears the niqab believing it to be obligatory, it is not permissible for her to remove it in front of non-mahram men except for a legitimate Shar'i excuse. If she removes it without an excuse, she is sinful. She also incurs sin if she does not cover her face and hands after the excuse ceases to exist. She must not leave her home except out of necessity. As for one who wears it believing it to be recommendable, she will be rewarded and does not incur sin by removing it. However, it is preferable for her not to remove it except out of necessity or need, as it is safer for her faith and further from temptation.