Code behind or aspx? Which one is the prefered way?

At my work we program all our applications using just c# code.  I have been looking into using the aspx pages to set up the pages I'm creating.
People here are saying its better to use code to do it rather than xhtml in the aspx page.  Which way is better to use?
What is the difference creating a whole page from the code behind vs just through the aspx side? I would love to program through the aspx as it is much faster to do so.


Thanks

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