The AAP actually recommends milk only for the first 6 months of a babies life. Other than the allergies, which is controversial, it is a pain in the butt to feed solids to a baby. It doesn't actually help them sleep longer, no. A young baby has such a small tummy that you risk them not getting the proper nutrients if they are eating solids. The reason for that, is because there are both more vitamins and calories in formula than in solids. They need to be able to still drink enough milk to meet their nutritional requirements, in addition to anything they take in in solids.
Now, as far as it being a pain in the butt, at 2 months old, they still push foods out of their mouth, so it's very messy, and a waste of money too.
Personally, I've found that it's best to wait until the baby is reaching for food on their own. My first started solids at 4 months, and was eating baby food until a year old. My 2nd I didn't start feeding solids until she was over 7 months old. She started reaching for foods on my plate, and I would give her my softer foods. We startedgiving her baby food then, and she only ate baby food for 1 month before transitioning to table foods.