If you have 2 parents that are honestly committed to the wellbeing of the children, it can work well. Generally it requires a cooperative relationship between the parents. In other situations it isn't even a healthy option. Divorce often involves one or both individuals who are dysfunctional in some way to begin with. Often legal joint custody between these types of people does little more than reduce the child to a psychological "chew toy."
I know the thinking, at one time anyway, was that it was important for a child's stability for there to be one parent who had the final word in disputes. With reasonable people there is a lot of room for flexibility in a sole custody arrangement. Of course, the key here is "reasonable" people. All too often those involved in custody battles are neither reasonable nor putting the child's best interest first.
I have seen joint custody work well, and I have seen it be a disaster, with the children having no sense of permanence with either parent. What you end up with is the perpetual involvement of the state and 2 or more families with their lives completely under their control, which, as we should know from any number of other situations by now, isn't looking out for any body's interests BUT the state's.
If I am not mistaken, I think it was Ted Nugent who had a great idea on the custody issue. The kids got the house and the parents had to be the ones moving in and out for joint custody. IOW, the kids need for stability and permanence was more important to them. I think that is a great idea.
I had a friend who had joint custody and it was literally 50/50 the kids spent half the week at dad's and the other half at mom's, they lived in the same school district. The only thing was the poor kids were basket cases. They were very angry and wild. Of course both boys were put on ritalin b/c they were "ADHD", they were 3 and 5 at the time. Maybe their behaviors were their only means of communicating the chaos in their lives because they did not have the verbal skills to express their feelings?? Could this possibly the reason so many kids are "ADHD"??
They never had the time to enjoy their homes because before you knew it it was time to pack up and move. The father was the better parent and should have received sole custody with liberal visitation imo.