You know... the heat from the lamp will cause a convection air current around the enlarger. The resulting flow of air levitates dust particles that will stick to the surface of the lens.... We certainly need a protection from this.
Right- I was just about to say that dust can indeed "fall upwards"!
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.