I agree with the PP. It depends on what your current situation is like, and what the point of pre-nursery would be?
I think 2 is a good age to start socializing in groups and to learn the things they `teach` in nursery school, like basic social ettiquette ie cleaning up your toys, sharing, paying attention to the teacher for short periods of time, playing together, etc.
Also, from what I notice about caring for my son, when he is exposed to other people( like my mom who is now visiting), he`s learning and experiencing different things than when he`s with me. So, even if your carer/nanny is great, it can`t hurt to socialise.
At the same time, I think that spending all day at a nursery is not needed at such a young age. half days or a few half days would be ideal in my opinion. That`s what I plan to do.