Virtues: A lot of the style rules are great guidelines.
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
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