Adding /o to regexps with no variable interpolation doesn't hurt anybody. It just ignored. I don't think it can be counted as bad style since there is no anything bad in doing it.
There are a lot of things that do nothing at all, and in my book still are bad style:
for (...) {
...
}; # semi colon
"This is a string literal that will be optimised away and doesn't real
+ly hurt run-time performance. Actually, string literals in void conte
+xt are an easy way of having multi-line (nested if wanted) comments (
+but don't).";
s/\</\./g; # both don't need escaping
$I_JUST_LIKE_USING_VARIABLES_LIKE_THIS = "and it doesn't hurt performa
+nce";
$I_JUST_LIKE_USING_VARIABLES_LIKE_THIS = "it is, however, very bad sty
+le";
I think I could think of many more examples of pieces of code that are bad style, but do work, don't hurt anybody and/or even are ignored.
I think it's bad to use /o when it's not needed, just like using escapes where they don't serve any purpose (note: escaping to avoid fscked-up syntax coloring is a valid excuse :).
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