Joel Oleson has posted an article on the subject of Crawling and it’s consequences. He also presents a solution to the possible problem of the Crawling process being a heavy one . . . to use a dedicated web front end server for Crawling.
“In SPS 2003 we found that indexing could be a pretty heavy weight operation. In a small/medium environment it’s not a big deal. In an enterprise environment crawling hundreds of GB to TBs indexing can potentially cause more traffic than user traffic.”
You can find this article here.