Spotlight is a piece of crap
Spotlight is a piece of crap. There, I said it.
My computer should run super fast. But if spotlight randomly decides to start indexing, suddenly everything slows to a crawl. Why can't it wait until I'm not doing something important?
I would update to 10.9 to fix this, but according to coolestguidesontheplanet, the spotlight woes persist in 10.9. They simply recommend deleting the spotlight index, which of course requires rebooting your machine.
What's more, spotlight has never worked well for me. When I search things from it, it wants to search every email I've ever sent. It defaults to searching the contents of files, so when I want to find Word, it pulls up every e-mail and PDF on my computer that has the word, "Word," in it, and since there is sooo much stuff on my computer, it slows down the search process significantly.
There's no clear way to tell spotlight to only search filenames by default, nor to ignore contents of files by default. You can't tell it to ignore groups of folders on searches performed from the spotlight menu; you can only take the draconian approach of removing certain folders entirely from its index. But then, what if I want to search those non-indexed areas?
Further if you turn it off, it breaks a lot of stuff, since Apple's system internally relies on spotlight to do things, often with horrific results. For example, one time it used spotlight to identify which volume to erase during a Bootcamp install, but since one of my drives was set not to index, it thought that was the drive, and this caused the Bootcamp Assistant to reformat my external USB hard drive rather than the USB stick that I wanted to make the Windows installer on! Sigh.