When taking a copy of the node template do you need to maintain the article tag that is in there When taking a copy of the node template, should you keep/maintain the original code that is in the file? 

Example the article tag.

nid; ?>" class=" clearfix"> etc..

What are the implications of removing this, if any?
Actually you're free to edit templates !


The theme's css might depend on some tags, especially the article tag, so you could lose layout/design
If you're a forward thinking brave drupalista you definitely want to keep title logic and the possibility of rendering all fields (and comments) and respect the view modes ;)