With an optical system that brings the aerial in the film plane into my eyes. Good for focusing, not practical for viewing large format images.
To add to this, some focusing screens do offer an aerial focusing spot, or a clear screen with parallax focusing. Good for very high magnification or other situations where there is extremely shallow DoF, and especially useful where any groundglass would scatter too much light.
I do use a digital device in my photographic pursuits when necessary.
When someone rags on me for using film, I use a middle digit, upraised.