Importance of filtering Air Compressor

Recently found my 6 gallon compressor from HF was losing pressure fast and I’d have to stop and start while pressure built up again. Assumed it was the compressor’s regulator so I took it off and found a lot of rust on the fitting and within the regulator.

The connection on either side of this were rust free thankfully so it was just a matter of taking this off and no extra work, guess this is what happens when you use (cheap) plated steel and not stainless or brass….