A while back the big 3 announced the adoption of a new relationship attribute for the header link tag in order to specify a preferred version of a page where there may be different ways to access it and to help avoid issues with duplicate content. It’s nice to have an option for when you take over a badly built site where there isn’t a budget to rewrite a lot of code and do a million 301 redirects but this is just a band-aid on a larger problem.
This is why architecture of a project is important and if you build it right the first time, you don’t have to worry about this being an issue. There are always times however that a bot will surprise you with some weird entry URL so as a guideline, it’s good to monitor your analytics and do simple 301 rewrites as they happen, if they happen. It’s good to know too that WordPress handles a lot of the heavy lifting for you already so if you have a WP site – you’re pretty much setup already.