What is Smart Connect Technology?
http://blog.dlink.com/what-is-smart-connect-technology/
What is Smart Connect?
With Smart Connect technology the name is somewhat self-explanatory. When connecting a new device to your router, Smart Connect can intelligently identify the device, decide what band would provide it with the best possible connection, and connect it to that band. This helps in two ways. First, it takes the guess work out of connecting your devices to the appropriate Wi-Fi band, since it’s not always easy to determine what band is best. Many people assume the 5GHz band is always better since it provides less interference for high-bandwidth activities like streaming and gaming. But when it comes to devices like older generation phones and tablets, connected home products and Wi-Fi Cameras, the 2.4GHz band is often the better choice, so you can save the faster 5GHz bands for the devices that really need it. The second benefit to the Smart Connect feature is that it will continue to balance the amount of devices in all 3 bands every time there’s a new device added to the network, ensuring that one band isn’t getting overloaded while the other two are completely empty.
這份文件所提到發生作用的場合，是"new device"(=連線建立階段)
所以"已經連線階段"的裝置，是不是可以受惠於這種技術？只能說廠商"沒講"！
可能有某些消費者"想像"說應該"全程(包括已經連線階段)"也會自動切回5G(是吧!?)
這種技術不是沒有，但目前已知實作比較完善的還是像Cisco這樣的網通領導廠商
