So, check out this thread. A theme that keeps coming up is people saying it's stupid b/c they can build a quiet PC that's cheaper/better. And many people focus on the noise @ idle, rather than under full load.
http://www.tomshardware.com/forum/id-3124466/compulab-airtop-fanless.html
That's what I'm talking about. Sure, if you just want a quiet PC, use quiet fans, water cooling, etc. But there are some situations where silence is worth the cost & compromises.
I have dust filters on all but one of my PCs with fans, and I have a well-ventilated, fanless machine built around a 10 W Apollo Lake board. I'll probably give it an annual air blast, but I won't have to open it to do so.
I don't consider myself to live in a dusty environment, but I had to clean the heatsink of my old P4 a couple times per year, or it'd overheat. That was my last machine of triple-digit TDPs with no dust filters. I've never had to clean out the machines with dust filters - just the filters. Their insides look completely clean.