Pros
None. Unless you like 10-hour days with no overtime pay or time off in lieu, stone age paperwork processing, micromanagement and deeply unpleasant bosses.
Cons
Tons of unpaid overtime - if you leave on time it is frowned upon. If you are a family person do not join REGN, they don't care. They will work you to the bone and your family and mental health come last, not first. Control-freak atmosphere. Cameras everywhere, the legality of which is uncertain. Interminable and pointless meetings. It is very hard to work in Regeneron Limerick because you're either in a meeting, replying to an email or replying to an IM, or doing all three at the same time, or firefighting some issue from a rubbish test method or something else which definitely won't be actual scientific progress. Endless, soul-sapping company internal propaganda about being a Great Place to Work (it isn't -demonstratably) and doing things the Regeneron Way (whatever that is, it doesn't happen in Limerick). Regeneron absolutely love themselves in spite of being a very small player in the greater scheme of big pharma.