"What Exactly Is It?
"If you go to Applications Accessories, you'll find the Tracker Search Tool in the list. From here you can do a full-text search against your files, and even refine by category.
"It's not a bad search tool, really.
"Throttle Indexing Speed
What you can do is configure Tracker to not use as much of your CPU, by going to System Preferences Indexing Preferences."