My parents have my sisters children. My in laws have younger BIL children.
Myself and older SIL use nursery or are at home.
For me, watching, I would say it changed the dynamic between them and my sister, them and BIL.
They become caregivers not grandparents, so with that comes a change in their relationship with grandchildren.
At things like family events, the children struggle with who is parent.
The boundaries are blurred I suppose. The nursery teacher doesn't turn up at Christmas lunch.
They get a lot of the firsts, which then causes resentment. Remember when x walked at granny's. Blah blah.
They become the contact point, school playground, play dates, etc.
So I suppose just being aware of that.