To add to what ExDilbert said, 5 GHz networks are less subject to interference, because they cover a shorter distance; they have more difficulty crossing obstacles. They also have a larger number of channels available, so your neighbours are not as likely to be on the same channel. This will help with your Wi-Fi speeds.
On the other hand, 2.4 GHz networks do have a longer range, but there are only 3 non-overlapping channels in Canada and the USA. The means that if you have many neighbours that have 2.4 GHz networks, there will be interference and will lower your network bandwidth for you and them.
Also, Wi-Fi 5 (also known as 802.11ac) networks only use the 5 GHz frequency, with dual-band routers using Wi-Fi 4 (also known as 802.11n) for 2.4 GHz support.
Personally, I set my network name to be the same for both bands, and I let my devices use the one that’s appropriate. They are usually smart enough to use 5 GHz when more performance is necessary and 2.4 GHz when they’re sleeping to reduce power draw.