It leads to a litterling of the world with useless Javascript. The correct way to achieve the objective is to use plain links and a robots.txt file in the root. If some crawler disregards the robots.txt file, you nuke that sucker from orbit. Javascript is evil. Javascript is the root of all evil. Badly written javascript (and there has never existed goodly-written-javascript in the entire history of the universe) is responsible for 99.999% of all safety and security issues since it was barfed-up by a moron.