Limitations:
minor:
Style rules shouldn't be followed when they make things awkward or harder to understand; that's more a problem with some readers than the book, but it's something to keep in mind...
less minor:
A lot of the grammar proscriptions are confused at best (and not followed by the authors themselves, in that work or others). Language Log has oodles of examples: http://languagelog.ldc.upenn.edu/nll
http://chronicle.com/article/50-Years-of-Stupid-Grammar/2549...
"Needless" gives a test you can apply to every word. "Omit words" sounds simpler, even obvious, but only because you know it's a shortened form of "omit needless words". We could shorten the advice to "simplify", but that doesn't give you the how.
It's a tongue in cheek response to the EoS quote ("Omit needless words"), not - devoid context - serious style guidance.
(I believe the parent quoted Twain.)