Widely known PHP module for minifying responses - Minify (https://code.google.com/p/minify/), as one step of it's minifying process, does something rather unobvious. It adds a new line after every opened tag, just before first attribute (if such is present).
// use newlines before 1st attribute in open tags (to limit line lengths)
My question seeks for pointing out actual reasons behind this action and cases when the overhead of plenty new characters in minified output is justified by actual gain from having your lines shorter.
I found about this taking place when I recently stumbled upon JSON parsing errors, which reason was not clear. The part of minification process makes JSON responses (these that contain html tags) invalid. Alike issues you may get when having inlined JS, againg containing the tags.
This is in the FAQ
Why do the CSS & HTML minifiers add so many line breaks?
TL;DR: Ignore them. They don't add to the output size and if you absolutely want all content on one line you will have to use another tool.
It's rumored that some source control tools and old browsers don't like very long lines. Compressed files with shorter lines are also easier to diff.
Since both Minify classes are regex-based, it would be very difficult/error-prone to count characters then try to re-establish context to add line breaks. Instead, both classes trade 1 space for 1 line break ( ) wherever possible, adding breaks but without adding bytes.
If you can think of another safe & efficient way to limit lines in these two tools without adding bytes, please submit a patch, but this is not something anyone should be worrying about.
Some email servers also automatically insert newlines after 1000 characters, which would break minified HTML generated with this script.