On the other hand, think for a moment of fume cupboards in chemical laboratories, or better, laminar-flow microbiological work hoods. Given that the work to be protected is at the bottom of the contained space, horizontal airflow above it is protective if the size/mass/velocity of contaminating particles is such as to prevent them from falling to the bottom of the space within the time taken for the air's transit of the space.

Still air demands total filtration/cleanliness, or the work can be contaminated by the effects of gravity on contaminating particles. Laminar flow allows for some contamination to be endured if the mathematics of risk are correctly evaluated. In conjunction with filtration of the inlet air, it can work a treat.

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Yes -- a lot certainly depends on the location (and nature) of the contaminants. In a typical home lab (yes, I am making assumptions here, but ones based on visits to a good number of home labs; dust seems to be a common companion), there's likely to be a fair amount of deposited dust on many surfaces. Blowing air in those environments virtually assures a redistribution of that dust, to the detriment of the disk platter. In still air, the rain of dust will be much more moderate, given the assumptions.

I agree that the best arrangement is filtered air, with a gentle circulation to scrub out particulates that evolve within the protected space. Semiconductor fabs are arranged this way, with the primary source of contaminating particulates in that situation -- humans -- properly isolated within protective suits.