Hey - not sure if this was covered already - but - for USA bound flights there is a security requirement that all passengers in a pooled group be present together at checkin to check the bags. This is solely a US requirement.
From the Swiss website - this is the phrasing used

"If you are travelling to the United States and wish to check in baggage, you must be physically present at the check-in counter."

I think the reasons are that when passengers are pooled, the answers to the baggage security questions are answered basically on a joint and several basis so that it is expected that items from any passenger would be in any other pooled passengers bag - so if you are going to be traveling together in a pooled booking then all of you have to be present with bags when dropping them so that all passengers answer the security questions together.

@orbitmic essentially mentions this and @adrianlondon - this may apply for non-USA flights.