Spare Parts is tricky. I wouldn't use any of the fancy settings that it lets you do, but I do find the Battery History portion to be VERY useful.
If I'm having a high % awake time, I load up the battery history, I hit 'total since boot', and look at 'Partial wake usage'. Also useful to look at sensor usage (Android System will use a lot if automatic brightness is set), CPU usage, and GPS usage. Some of the options don't work, but it's good to get a gauge of what's eating your battery.
Having it installed does nothing. Literally. Except for take up some space in your memory. But it's a very useful tool for me on my Eris.