Not useless. (caveat untested code) Say you have a css:

Warning.*{
  color=#YELLOW
}
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and you code in your html

print "<SPAN CLASS="WARNING">"My warning</SPAN>";
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all over the place, and then your phb says "make the warning section have a blue backround", all you have to do is update your css and then with no code change to current code base and a simple one line update to the css you're done!