This has its primary uses in linking a question on the site with any discussion about the question on the Meta site. This gives a simple way so that people on the main site realize that there is discussion about that specific question that may warrant their eyes to investigate.
However, this is really the only guaranteed pertinence, and half the time users are hesitant to link the question on the Meta site (usually because they don't want to point fingers). If it's also a serious discussion, there is often a comment on the post that provides a link to the Meta discussion, resulting in some level of redundancy.
My largest issue, though, is that many times a link on Meta will not be on discussion about the particular question that is linked. It could just be a reference as an example, and sometimes it's just quoting from something that happens to be on the main site. These instances are fairly common and do not serve a substantial benefit to browsers of the main site to view at within the context of the linked question.
So I don't see a lot of benefits, as there is one benefit it does serve but that benefit is easily handled by a comment.