DrDoc - 8:09 pm on May 6, 2013 (gmt 0)
There's also a big difference between something being allowed and something being good practice.
Despite periods being allowed in path names and file names, one can argue whether it is a good idea to employ periods in the names. And, if one never uses periods in such names, [^.] becomes acceptable (and, indeed, preferred ... for that particular user or circumstance).
While I agree that micro optimizations may not always seem worth it, the greater issue here is being able to always write optimized regular expressions. There are some expressions which, when executed on a short string, run very quickly but when run in a different scenario take f.o.r.e.v.e.r to execute. The problem is the prevailing habit of copy-and-paste coupled with the mindset of "it worked in this instance, so it must work in the other".
I think it is important to always write optimized code/regex/whatever, simply for the fact that it is a good habit, even if they gain is not immediately (or ever) realized. There simply is no drawback to an optimized version (assuming it is in all other aspects identical in serving its purpose).