Dropping FK Constraints In A Stored Procedure

I just looked at a coworker's stored procedure and this person is
dropping 4 Foreign key constraints and then re-adding them after
processing the required logic (updating rows in the 4 tables in
question).

Is there *ANY* good reason to do this? What are the performance
implications of doing this - negative or otherwise?

I was furious when I found this because every once in a while I would
notice that the constraints would be in flux....some days they were
there, othere days there were not. I mean, this is a good enough reason
to NOT do this, but I need some additional feedback. Maybe there *is* a
good reason, and that the logic just needs tweaking.

Thanks.