Having one credit card or account that you share with an adult child can be helpful. I have known parents who because they were able to access their adult child’s account were able to solve financial issues when the kid was abroad. My daughter still has one credit card that I pay and she uses it when I want to treat her to something. So for us it makes gifting her a special meal or item easy without me physically being there.
On the other end of the spectrum, when my mother in law was no longer able to do her own bill paying, a joint account was required so my husband could pay her bills and handle her finances for her (without getting full power of attorney).