This is Off Topic because I want to make it clear that I'm musing.
Big fans are absolutely ideal area coolers. They're simply outstanding. Every case needs area cooling.
Certain small, hot components don't benefit the way the rest of the case does from area cooling. Since I don't do video cards, I'm talking HDDs and the CPU - this is the arena of spot cooling.
A good fan for spot cooling should be as large as the object being cooled, but no larger (or at least very little larger). The garden-variety 3.5" HDD is 101.6mm wide; a Scythe 100mm fan makes an ideal spot cooler for it - and using push-pull (as I do) one fan can cool two HDDs. That's what I've been doing for a while now, and it works very well.
For a long while, I've used passive Ninjas to cool my CPUs. The area-cooling fan provides the gentle breeze needed by the Ninja. At this time, the mid-tower ATX cases that come with 220mm side fans cannot mount a Ninja. So until these cases get an inch wider, a 126mm HS or HSF is about the tallest that can be used. Hello, Freezer 64 Pro! But these smaller heat sinks come with closely spaced fins (Scythe decided not to put their dwarf Ninja into production, darn it!). A gentle breeze won't push much air between tightly packed fins.
So the 104mm-wide 64 Pro is a candidate for spot cooling. I've already tried, temporarily, a 100mm Scythe fan and it worked well. And now I come to the point: I'm considering putting a fan back on my 64 Pro, and leaving it there this time.
With a CPU fan, I can turn the big fan down close to the starting voltage and get more than adequate area cooling - I'm talking good
area cooling. And I can concentrate on providing no more spot cooling than is necessary, where "necessary" is an individual judgement about CPU temperatures.
In other words, I think adding a fan will result in a quieter computer because the big fan can be run more slowly.
Hmm. Upon reviewing this, I started with this sentence: A good fan for spot cooling should be as large as the object being cooled, but no larger (or at least very little larger).
Come to think of it, the big fan is a spot cooler for the case! AKA area cooler, where the case innards are the area. And the big fan darn near is
as big as the case!