I found several times tags like these, and sometimes I found a more appropriated tag, sometimes I don't, but when I do I'm confused. Should I use both tags, the more appropriated and the one that has the message or should I only use the one that I found more appropriated? I kind of read that message as "don't use this unless it can be helped" but maybe I'm wrong?
I read that as "Use a more specific tag as well, if appropriate". This is in line with the general tagging guidelines, specifically these points (emphasis mine):
Pick tags that show higher counts in the look-ahead prompts, as they are more likely to make your question appear highlighted for a user on the main page or show up in someone's RSS feed.
At a minimum, try to include at least one very broad tag (i.e., java or c#) and one other tag to narrow the topic down within that broader category (i.e., strings or garbage-collection).
You are limited to 5 tags, and you are generally better off trying to use all 5 of them (if there are 5 appropriate matches among existing tags).
I read that as suggesting that broad tags are good. If another tag is applicable, by all means use it, but if you still have tag space left over, include the generic one as well. Broad tags such as hardware are useful since people may be following them who are interested/experts in hardware stuff in general. That makes your question stand out to them and makes it so much more likely that you will get an answer.
That kind of advice on a tag wiki excerpt tells you to try and find a more specific tag as well but not, to my mind, to avoid using the tag in question at all. Tags with that advice tend to be very broad and not very useful by themselves. They should be combined with other tags to narrow the scope but tags are not mutually exclusive. In general, more tags are better than fewer.