Buyer representation Agreement.... Is it needed?

[Vamshi Ananth]

Being a buyer is it mandatory to sign a Buyer representation Agreement with your Real Estate Agent?  My agent suggests I sign it in order to work with him and for him to put an offer on a property.  Is this a common practice? 

 My concern is am I locking myself with a just one Real estate Agent to represent me for a set period of time... where I don't have the freedom to pursue other properties with other Agents? 

Has anyone signed such a document before? What are your suggestions on whether to sign it or not?