
Originally Posted by
Daniel Browning
Aside from the obvious (protection, portability), there can be several reasons. For me, it's mostly a matter of noise. I buy sound-dampening cases (Antec) that go a long ways to lower the decibels of my water cooler fan and raid array. Lower noise helps my sanity as well as audio/video post-production.
Another issue is cooling: in a still room, the convection alone (and/or turbulence from nearby component-specific fans) may not provide sufficient cooling for components that lack their own cooling fan. In a case, the power supply fan and case fans generally ensure sufficient air flow and turbulence over such parts (e.g. south bridge, video card, hard drives, etc.).