Here's just my 2-cents on this:

- color highlighting improves clarity and readability of code, hence improves clarity and readability of the edited post, makes it easier to read ([related post][1]).
- they're not destructive and don't alter original content
- they change wall-of-text code into easier to read code (bullet point 2 from [here][2])
- posts where multiple languages are used can benefit from added syntax highlighting; in fact, I frequently post answers that provide solutions in bash, perl, python, and others, and syntax highlighting helps distinguishing the syntax of each solution.
- merely using tags as [dessert's answer][3] suggests can work for single-language posts ( IMHO ), but not in multi-language posts, plus [as Zanna pointed out][4] - tags can be removed. 

Personally, I see absolutely no problem whatsoever with such edits. In fact, feel free to edit my answers any time just to add syntax high-lighting. I've like 1699 answers by this point, and prettyfying that many is time consuming :)


  [1]: https://meta.askubuntu.com/q/15434/295286
  [2]: https://meta.askubuntu.com/a/103/295286
  [3]: https://meta.askubuntu.com/a/17453/295286
  [4]: https://meta.askubuntu.com/questions/17449/what-to-do-with-language-bash-edits/17453?noredirect=1#comment36232_17453