When you open an app, its window only stretches from the top of the display to the top of the Dock, so you’re missing out on some valuable space. By default, macOS displays the Dock at the bottom of the screen, and it’s always visible. When you’ve got limited screen space available, it’s a good idea to use every pixel of it. Fortunately, macOS offers a 'full-screen mode,' which you can use for most of your apps. On the contrary, if you have a smaller Mac, like a 12-inch MacBook, there’s not much room for multiple windows, and you may want to make each one as large as possible. You can have several windows visible, large and small, each organized efficiently.
If you have a capacious 27-inch iMac, you’ve got lots of room to stretch out. The size of your Mac’s display can affect the way you work. Software & Apps How to Enter and Exit Full Screen Mode and Use Split Screen in macOS
