Dennis,

My Kia and many other cars use GDI engines (Gasoline Direct Injection). My Kia is pretty peppy for being 2.0 litre and my GF's car has the same motor, but turbocharged making close to 300HP. I found the following web page talking about this:

http://www.thetruthaboutcars.com/201...in-a-nutshell/

The paragraph I found most interesting, as it relates to this thread, is this:

Due to modern unburned hydrocarbon (UHC) regulations, vapors from the crankcase are usually vented into the intake stream in order to prevent oil droplets from escaping through the exhaust. In a port injection engine, these droplets are ‘washed off’ the neck of the intake valve by a relatively constant stream of gasoline droplets. In a GDI engine, the gasoline doesn’t touch intake side of the valve. As a result, the droplets have a tendency to bake onto the valve and significantly reduce performance. To add to this effect, many advanced GDI engines also include exhaust gas recirculation in order to lean out the combustion mixture and reduce in-cylinder temperatures for certain combustion modes (reducing NOx emissions). Since GDI combustion has the ability to produce far more soot than premixed combustion (port injection), the problem is magnified.

Even more alarming is that these deposits can dislodge and damage other downstream components (turbochargers, catalytic converters, etc.). Manufacturers have added systems to capture these oil droplets and particulates, but no system is 100% effective.
So, it seems, this little filter is pretty important... on this type of motor at least.