The packages tag seems to have originally meant to be used for questions about package development, or general questions about using packages (e.g. how to install a package?)
I noticed that it is often added to questions which ask about how to use some specific third-party package.
I would like to discuss this usage a bit. I'll tell you my opinion, please comment if you disagree or if there's something important to add.
First, I don't think there's much value in using packages for specific questions about specific packages. An example would be: "How do I create a multi-panel figure with SciDraw?" I propose to reduce/avoid such usage. For such questions, the tag is not specific enough to make a useful category or search option. But it does dilute the first type of use, e.g. questions about package development.
An example of such an (IMO undesirable) usage is this (screenshot in case tags will change in the future):
Second, I think there is value in introducing specific tags for large, complex and high profile packages. There are already a few such tags, and today I created two more, namely ncalgebra and xact. Earlier I created scidraw. The big question is of course: which packages should get their own tag?
I think the examples I mentioned definitely need it. xAct and NCAlgebra are large and complex packages with a lot of functionality accumulated during continuous development for over a decade. Questions about them usually require domain specific knowledge, familiarity with the package as well as with Mathematica. It helps to be able to easily browse these questions when learning to work with such a package.
Most importantly, there are already multiple questions from multiple users about these packages.
I think we can use this latter criterion for creating tags: several questions from different users over an extended time should warrant a new tag.
There is one more reason why giving packages their own tag is useful (admittedly I have a bias here): it helps the package author to find the relevant questions. I did not create the matlink tag, but as one of the authors of that package, I am very glad that it exists. It helps me filter relevant questions and helps reduce the support load. In fact since this week we suggest M.SE as a support option for MATLink.