One of the problems might be that humans tend to be not very consistent over longer periods of time. So choosing a set of tags which will stay useful for, say,

One of the problems might be that humans tend to be not very consistent over longer periods of time. So choosing a set of tags which will stay useful for, say, 10 years is hard. Because of this "tag rot" is likely to happen. After a long time, when you're looking for a certain file you might not remember the tagging scheme you applied at the moment you tagged the file you're looking for.