A lot of good points on here already. I have one to add--when a spouse/parent/child dies, an extensive support (physical and emotional) system is already in place. Another--elder care (including requiring the elder to keep actively living!) is easier.
We're looking at multigenerational close-to-each other living with several branches of the family, rather than all in the same house. So far the grandkids (my kids) love easy access to their grandparents, who love being able to send them home when they're done spoiling them!