What is the purpose of the VisitorIdentification control?

Question

My Sitecore starterkit website contains the following control in the head of each layout. Can someone explain what it's purpose is and whether or not it's needed? I could not find any information on it on the Sitecore SDN...

<sc:VisitorIdentification id="VisitorIdentification" runat="server" />

Control's output:

<link href="/layouts/System/VisitorIdentification.aspx" rel="stylesheet" type="text/css" />

Contents of stylesheet:

.sc_visitor {
}

Answer 1

See Analytics Configuration reference, paragraph 4.1.5 "The VisitorIdentification Web control".

Just in case the link about becomes obsolete:

The VisitorIdentification Web control helps the Sitecore analytics engine identify robots. The VisitorIdentification Web control generates an HTML <link> element that references an empty CSS resource. The Sitecore analytics engine uses this request to help differentiate robots from actual users.

For more information about automatic robot detection, see the section Automatic Robot Detection.

Important

To assist the analytics engine in robot identification, include the VisitorIdentification Web control in all of your layouts. For example:

<sc:VisitorIdentification runat="server" />