one of these things kind magically "appeared" last time i took apart a Medecoâ„¢ mortise ,too.

i never really even realized where it had come from until today.
i reassembled my last one w/o this part,and it seems to work fine.
is this part even needed in a lock simply meant for picking?
what is it for?
where does it go?
what does it do?
thanks for reading.
awol70