I've found several question which is tagged with the phone model of the poster, but the tag does not help describe or classify the question. Example 1 2. In those question the tags serve no other purpose than to inform the reader of the user's phone model (in case it matters). This is in contrast to this question where the phone model is a relevant sorting/classification criteria for the question.
There’s been a major uptick recently in tags that are not useful and just add noise. I want to stress that these are usually added in good faith, and I am not questioning anybody’s motivation – I know that they all mean well. But this particular category of tags is one that has been historically referred to as meta-tags on MSO, and these tags cause a lot of problems.
The reason meta-tags are a problem is that they do not describe the content of the question. They describe some other aspect of the question, like the author’s skill level, or the author’s motivation for asking it, or generally what “kind” of question it is (poll, how-to, etc.).
Meta-tags are actually a subset of a larger problem that I usually call dependent tags. These are tags that don’t say anything by themselves – you can’t tell what the question is about unless they’re paired with some other tag (or several of them). These tags are a problem because people don’t realize this and will often use that as the question’s only tag.
The point of tags on Stack Overflow is to help other interested persons find your question by sorting it into clear, specific categories. This is not the same as indexing or summarizing the question. The differences are subtle, but important.