<p>For many fields, it’s a common attitude to advise undergraduates to move to a different department for grad study, they say in order to get a different perspective. This is common at many, many schools. Some fields and departments LOVE to take their own for longer, such as certain departments at MIT. It varies, but you can assume with no other knowledge that studying elsewhere would be beneficial (although obviously talk to people/profs/etc).</p>