Why would split custody be used?
Split custody is not very common. Essentially, it's like awarding sole custody of one child to each parent.
For instance, perhaps a couple has two daughters. One is 10 years old and the other is 5 years old. In a split custody arrangement, the mother may get full custody of the 5-year-old girl, while the father gets full custody of the 10-year-old girl.
In some senses, this can make life easier for the parents because they get to focus on just one child and they don't have to work together to create custody schedules, parenting agreements and things of this nature. However, it's also frowned upon because each child will have almost no relationship with the other parent or the other sibling.
The reason it may be used in rare cases is when scheduling and other factors make life easier for the kids. For instance, the 5-year-old and 10-year-old likely don't go to the same school. If Mom lives closer to one school and Dad lives closer to the other, then split custody cuts down on travel time and means neither child has to leave her school, class, peer group or extracurricular activities.
After all, the court does want to focus on limiting the amount of change in the children's lives. In most cases, that means joint custody so that family life stays as close to the same as possible, but outside factors are considered.
This helps to show why it's important for parents to know all of their legal options when determining custody. As always, the children's best interests should be the focus.
Source: FindLaw, "What's the Difference Between Split Custody and Joint Custody?," George Khoury, accessed Jan. 19, 2018