Having kids close together is also a legitimate strategy for having closeness among siblings. Not a guarantee, but having them in a similar stage of development can help them play better together (older kids aren't always interesting in what younger kids are, also there are physical differences that can make sports no fun for older kids). There's a practical aspect here. Not for everyone and it also varies a lot based on the temperament of the children. The strong outside influence on my family to half multiple was that we were able to see a good number of examples of large (>=4 kids) families that were an example of what we wanted too.