I hyphenate if my Sims marry but that creates the problem with the surname field not being long enough.
One of my favourite Sims, Anaïs Dembele is a scientist and explorer. She's accomplished probably more than any of my other Sims, and explored from the bottom of the Sulani ocean, to the jungle and to Sixam. She saved Strangerville and she's "king of the lab" (little Bones reference there). She owns 2 homes and a thriving business/cultural museum, written books and maxed most of the skills. When she got married to military Captain Joel Paulson I wanted to hyphenate her name as IRL I think someone like her would still want their name to go with their accomplishments. I couldn't, it won't fit. So I had to leave it as Dembele. Then they adopted little Etta. So for her I just had to squish the names together DembelePaulson. So yeah, box really needs to be bigger.
If I create a family I give them just one name but particularly for writers, actors or Sims that are recognised for certain things I hyphenate. I often create a sim with the intention of them being a future partner and now I count the letters in their name so it will fit if they get married lol.
I also wish we could add professional titles such as Dr, Professor, etc (I once worked with someone who was Sir Professor Dr but that would be waaay to complicated) but that's maybe a conversation for another thread!