http://msmvps.com/blogs/laflour/archive/2009/03/05/sharepoint-tip-18-do-you-know-why-to-use-dedicated-web-server-for-crawling.aspxBy default, Office SharePoint Server 2007 uses all of the front-end Web servers in the server farm to crawl content in the same server farm. The index server sends requests to each front-end Web server in the farm. The front-end Web servers get the requestedenCommunityServer 2008.5 SP2 (Build: 40407.4157)