Nothing is what I use those things for. You just need to understand that OS tweaking is a dying art, because it's less and less necessary anymore with the explosion of fast and cheap CPUs, memory, and disk space.
Generally speaking, even though it may seem like Vista is considerably slower than XP, truth is, most dual and quad core systems are sitting around twiddling their thumbs waiting for something to do. CPUs may not be getting faster in terms of raw clock speed like they used to, but with the advent of parallel processing, processing power is actually expanding at an even faster rate than before. And DDR2 RAM prices are dirt cheap these days, plus you can find 1TB hard drives going for less than $200.
There just isn't a lot of real need to spend hours trying to tweak every last thing about your system trying to eek out just a little more performance. There's such a glut of available resources, you can afford it. So stop obsessing and try using your system for something fun and enjoyable.
How do you use: View performance details in Event log, Openreliability and performance monitor, View advanced system details in system information, and generate a system health report.
And what do you guys use these for I have been using the help files and I still cant do that much with them.
Chowhound
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GameSpot
Giant Bomb
TechRepublic