I have encountered for several times that some users have complained to me the use of Unicode characters (of normal series and normal shape, i.e. not bold nor italic) such
→, claiming that “some browsers may not have such fonts to render these Unicode characters correctly.”
However, when I looked up in MathJax font support, it is explicitly mentioned that “MathJax will download the necessary webfonts and fontdata dynamically…” and the default font is MathJax TeX, which does include all the necessary characters (It also works for mobile versions). And in MathJax browser compatibility, it says that MathJax’s HTML-CSS output has been tested on IE 6.0+, Firefox 3.0+, etc., which means there should be no compatibility issues at all.
So why do they deprecate such uses citing compatibility issues at all?
Edit: Here all characters are meant to be enclosed by math environments, so the possible compatibility issue is not about native font-rendering function of browsers.