You name 2.4GHz and 5GHz Wi-Fi the same SSID because of the idea of seamless roaming between the two bands. Well, the truth is your device may not be so good at deciding which band is the right one for you.
If you use the same SSID for 2.4GHz and 5GHz bands, instead of automatically switching to the better and stronger network, your device will keep connected to one band until it is too weak to be connected. What makes it worse is that you cannot switch it manually to the other band because they use the same SSID.
Separating the two frequencies as two different SSIDs has more benefits. The 2.4GHz travels further but is more susceptible to interference, while the 5GHz offers faster speed. In reality, all your devices hang on the 2.4GHz connection and never switch back to the 5GHz. If both have the same SSID, you cannot switch yourself manually. Imagine how frustrated you would be when you want to connect to the 5GHz for smooth online gaming, but your device stays on the 2.4GHz and you cannot change the network manually.
In short, the best practice is to have separate SSIDs, with frequencies chosen to match the device and the task at your hand.