In my opinion the first few years of school are a decent time to homeschool. There is no way to say what's best for any one kid/family, but there is a very small skill set taught in the first few years. The major subject is reading. This is a subject where one on one time is highly productive and group activities tend to be not as effective. As an example I have an aunt that didn't learn to read till she was in 4th or 5th grade. She got by through memorization of the story books as they were read to the class. When it came time for her 5 minutes with the teacher she could spout the story back and pretend to be reading. If it was a book that she hadn't seen she would look at the pictures and guess. None of her teachers figured out she couldn't read till she was almost done with elementary school. This doesn't happen if mom is spending hours per day, one on one with her child.
As for socialization, I can't tell you how many times my bully avoidance skills have saved me from a near certain pounding at the office. I went to public school and ended up as a physicist, so obviously there is absolutely no socialization benefit to attending public school. (How's that for anecdote.)