I'll venture a minority opinion (I'm in mathematics, where the culture is very possibly different than in other fields).
As a referee, I have an instinctive negative reaction if I know that an author has taken the time and effort to conform to a particular journal's style. The grounds for this is that most journals employ typesetting staff for this purpose. Especially considering the very high price of many (if not all) journals, for authors to refuse to do this suggests to me a principled refusal to waste their time.
That said, I can see that many people hold the exact opposite opinion, and even that my own feelings may be a little bit silly. So I certainly don't actually hold this against authors when evaluating submissions. (Indeed, if I receive something formatted, I never know if it is the author or the editorial staff that has formatted it.)
My impression is that most (but maybe not all) mathematicians wouldn't hold it against you if you don't bother. Moreover I believe that most mathematicians in fact don't bother with such formatting guidelines.
I have never heard anyone voice @jakebeal's opinion before. Of course, counting the upvotes, he speaks for at least eight other people! You might take this as evidence that the answer to your question is dependent on what your field is.