Do I need to know Wayland?

Do I need to know [about] Wayland to use a Linux system? No, Wayland is just a low-level implementation detail.

Do I need to know Wayland to develop an app for Linux? No. Again, Wayland is quite low-level. For developing apps, use toolkits, such as GTK+ and Qt. They abstract away the details, letting you focus on developing the logic of your app.

Do I need to know Wayland to be happy? No, but it may help.

So, who needs to know Wayland? Mostly developers of toolkits and compositors.

Why would I want to learn Wayland anyway? It may just be interesting.