What do the Bots do?

I am curious what the bots that are registered users on the site do. My only experience with bots is in online video games and my understanding of them are that they are generally not allowed. Being that I haven't read anything about trying to remove them on the site I am forced to believe that they are allowed here. So what is it they do? The bots I'm writing about are Baidu [Spider], Google [Bot], and Yahoo [Bot]. There are others also these are just the ones on right now.

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