In TeX.SX the tags XeTeX and XeLaTeX are the same, but there is a big diference between this two topics, so when we look for something specific we get also results of little help. The same case happens with LaTeX an TeX. Thus splitting in two separate tags is of use, more opinions like this one?
The tagging approach taken here is quite deliberate. Whilst TeX-sx covers the TeX world generally, LaTeX is by far the dominant format in use (plain TeX and ConTeXt are much less widely used). As such, it was clear from the earliest days of the site that questions should be treated as about LaTeX unless they are explicitly not. Thus we have tags such as plain-tex and context, plus for low-level questions tex-core.
For engine variation, we have tags pdftex, xetex and luatex. These are used to show that a question is about that engine specifically but do not specify which format is involved. Thus a question which is about a questions specific to using the plain format with the XeTeX engine should be tagged both xetex and plain-tex. (The latter tag is used not just for Knuth's TeX90 format but any of the 'essentially plain' derivatives.) On the other hand, a question specific to XeLaTeX should be tagged xetex plus whatever packages are important (likely to be fontspec or perhaps fonts, though it could be of course a question about drivers or the like).