JD_Toims - 12:47 pm on Jul 31, 2013 (gmt 0)
This is completely unnecessary if the correct header responses are returned. Better test your response codes properly.
All my error pages get noindexed and have for years, because Google has been known to "glitch" on occasion, sometimes headers get over-written inadvertently after testing (especially with a complicated .htaccess and php redirects -- been there), but mainly due to Google being "cold molasses slow" at removing 404 pages from the index.
So, technically it's unnecessary, but in reality it's been a nice backup to ensure what's supposed to happen (page gets dropped from the index) happens as fast as I can get it to, even if something "goes wrong" on my end or theirs.