Dust

I don't but it's probably a good idea. I live in AZ, and it's very dusty here.

I use silks. Very old now. Silk won’t hold dust and it won’t scratch because of it. My wife can stitch a cover in 45 minutes. I can cut a drape in 5 minutes. Silk does not fray, it is water resistant and can stand a pretty good amount of heat.. I have silk surrounds that are over 75 years old. Covers over 50 years old.. Change the covers for the seasons..
They will last forever if you just soak them in Woolite in a 5 gallon bucket and rinse.

Mine still look brand new.. folks come over for a concert, I uncover and polish all the gear up in 5 minutes with micro fiber towels. Everything stays waxed and chrome is protected with Never Dul

I cover components with exposed tubes. I use a large size polishing cloth, the type for cleaning cars or motorcycles.

I too live in AZ and dust is to us as mud is to others. 
I have a sheet that covers the TV and all components
Individual socks for each speaker.

Do they help? Yes. 
Final solution? No. 

But you dust 1/2 as often.

Assuming you use them.