This old rule is certainly a tricky one. It’s a favorite topic of editors everywhere – it appears in all of these lists of rules it’s okay to break: this one, this one, this one, and this one. Oh and also this one.
Many of these lists put this rule right at the top. In fact, I did a Google search for “Grammar rules it’s okay to break” and it showed up in every single article I looked at. So, I think it’s safe to say you can break this rule.
Why is this a rule in the first place and where did it come from? (A few of the articles linked above ask the exact same question, probably to be ironic since it ends with as preposition.) One theory: prepositions are always naturally linked to a word in the sentence, so it would seem natural to put the preposition next to the word it’s linked to (the word to which it is linked?)
However, in practice this can make for some really awkward sentences. For example:
Who are you talking to?
I have nobody to dance with.
That’s what I’m talking about.
Now “fix” them to get rid of the dangling preposition:
To whom are you talking?
I have nobody with whom to dance.
That is the matter about which I am talking.
See? They just get awkward, stilted and pretentious sounding.
The one time when dangling prepositions become a problem is when they are absolutely unnecessary, as in the sentence “where is he at?” In these cases, simply follow Strunk & White’s famous rule, and omit needless words. Otherwise, prepositions are perfectly fine words to end on.