From a teachers perspective and someone who has worked in child care/preschools etc there are many benefits.
The main benefit is social development, it is a great opportunity for your child to start learning how to interact with other children, adults and have new experiences that may not be available at home. For example painting and messy play might be something you avoid at home for obvious reasons but at a preschool/care facility it is often encouraged and expereicned daily. (well at least at the places I have worked).
It can also be a good way to develop independance and get children used to seperating from primary caregiver for a while. This might scare some of you but when you get to school and your child is ok to stay and you see the mum/dad with kid hanging off their leg and the teacher prying them off 9ok i might be exagerating here) but u get the idea. Half days are especially good for younger children and can build to a day at preschool later
Aside from that u may find ur kids make friends and u can catch up with other parents/families so a good way to network. On the flip side it can be expensive and there are ways to get the same benefits for example - playgroup or start your own parenting group. You could meet once a fortnight and there are a ton of websites with great activities and ideas that you can use.
And OMG sry for the essay!! But child developement is a bit of a passion of mine!
I agree that the things you have mentioned are beneficial. But I don't know why they wouldn't get those things at home. Social interaction, an understanding of rules and taking turns, an understanding of how to interact with adults, an understanding of empathy and acceptable behaviour, messy play and free play, and perhaps more importantly an understanding of being important and of the wider world in general. Aren't those the benefits of staying home?
Thinking of the restraints and disadvantages to childcare compared to the things you can do with your kids at home, childcare for a 2 year old seems unnecessary to me (unless you want that time alone as a parent).
I agree too with Happy Head. If a child takes a few days to adjust to school (which would be normal for anyone, even adults need time to transition to new things) then why does this automatically mean that this child had never been to childcare? And the ones that do adjust, why does that mean that they necessarily went to childcare? I would have thought it was more of a personality issue than anything else.
I also don't see why a 2 year old "needs" to learn separation. Why? They are only 2!