For myself, I include everything, marriages, divorces, adoptions, etc. The
adoptions are in the tags which can't be seen. Only once have I taken
anyone off the tree. My great-aunt insisted I take her daughter's first
husband off the tree. I did so under protest and am still not happy about
it. Oh well...
Probably for that reason, I'm firm about being as complete as possible.
I'm also the repository of family photographs so I need to know who might
be on those photographs even if they are no longer part of the family. They
were still part of the family at that time and part of its history.