What is the point on the FAN cover vs no fan cover? Is this just cosmetic or is it functional as maybe a prefilter?

[miogpsrocks]

 

 

 

or 

 

 

[saarg]

It protects the fan, or your fingers. It's there so objects doesn't get stuck in the fan.

[burtjr]

Like saarg stated it's more of a safety item. almost no filtering qualities at all, but will collect dust and will need to be cleaned periodically.

[zonderling]

I prefer not to use them, without there is less noise.  With them airflow gets obstructed a bit and that causes background noise.  Obviously only delete them if you can be fairly sure nothing will get stuck in them.