The Live View and WYSIWYG (What-You-See-Is-What-You-Get) is one of the great advantages of capturing images with a mirrorless camera.
When capturing images with a DSLR the ‘optical view’ is NOT what the camera records. The advantages of a WYSIWYG view means that we can use the exposure compensation dial to ensure accurate exposure every time and never miss a shot. The live view also means that we get to see the depth of field that our chosen aperture will give us before we capture the image. Unlike a DSLR the lens aperture of a mirrorless camera is NOT held wide open when viewing our subject to ensure a bright view in the viewfinder. The EVF or LCD of a mirrorless camera will show us a bright view of the scene regardless of the lens aperture we choose.
There are instances when the WYSIWYG view of a mirrorless camera is NOT what you want to see, e.g. when you are shooting in a dark studio and using off-camera flash. In this situation if you do not adjust your Setting Effect option in the menu, then all you will see is a dark seen in the EVF or on the LCD, which will make it difficult or impossible to frame or focus your subject.
This is when you want your mirrorless camera to behave more like a DSLR and just show you a bright image in your viewfinder, regardless of the ambient light and the exposure settings you have chosen for the flash. This is when you want to go to Live View Display > Setting Effect OFF.