DD went to a day nursery from 9 months as I returned to work. For me the biggest advantage were:
interaction with other children as she is an only child
interaction with other adults
having access to activities I do not like to do, all kind craft related, I shudder at the idea of it, toys I don't need to get, outside space, learning to be independent
We did and still do lots of other activities with her like going to places, being physical active, incorporating learning into daily life like reading signs when shopping, DD learned numbers by "reading" numberplates, playing board games, doing jigsaws and above all, reading and talking to her.
I personally don't like typical nursery schools. DD is a Summer born and went to school 6 weeks after her 4th birthday. I didn't like the idea of structured learning from 3 onwards, it may be different for an autumn born one who often is bored in a more play based environment, so it may depends a lot on the chidl.
Learning is for school in my opinion, day care is for playing. Knowledge is absorbed in any setting, a day care setting is doing it in a more play focused way.