There are some reasons why five-pins socket is more popular. 1. Five-pins socket has more reasonable use of space resources. Just imagine it, if a power outlet has only one two-poles or only one three-poles, we won’t be able to utilize the space well. 2. Five-pins socket is more economical. It's obvious that, in the same scope of use, we only need one five-pins socket to use two-poles and 3-poles in the same time. 3. Five-pins socket is more convenient. Unlike common single three-pins or two-pins socket, five-pins socket has more choice.