In the same vein as Doitsu, it can also be useful when a large number of <span> are using it or when an aberrant use is made of it.
I know that here we are all more or less expert, and that we avoid this kind of situation, but when we try to repair a book... from the internet
, conversion problems or the use of poor quality WYSIWYG editor are common.
And then it's not a big highlight red. The example of Notepad++ is excellent: discreet, but easily visible if you look for it specifically.
(Obviously to the extent that it can be implemented)