Tefillin on both arms not simultaneously

Question

Why do some people wear tefillin on both arms (not simultaneously)?

Answer 1

There is a dispute about whether strength or writing is the deciding factor in determining which hand will be used to wear tefillin. Therefore, some who perform all labor with one hand and write with the other, have the practice toward the end of davening to remove the shel yad and put it on the opposite arm for a few minutes to be mekayem both shitos. For more resources: https://vaadmhk.org/tefillin-the-right-way/