A title to a question should be edited if there is a spelling, punctuation, or grammar error. A title should not be corrected for style, as long as the title adheres to a correct standard. A title should be rewritten if it is nonsensical. Personally, if I find a nonsensical title that, after a few readings, I figure out what it means, I do rewrite the title for the OP, to try and provide assistance.
There are actually two standard styles for titles, both of them equally grammatically correct. There are some exceptions to the basic rules I'm going to lay out, but I'm not going to list them all (They're pretty specific to certain situations that I doubt would come up here.). The two accepted styles of a title are the headline style and the sentence style.
The headline-style title reads like this:
Mneumonics That Work Are Better Than Rules That Do Not
Singing While You Work
A Little Learning Is a Dangerous Thing
The Editor as Anonymous Assistant
In the headline style, capitalize the first and last words in titles and subtitles, and capitalize all other major words (nouns, pronouns, verbs, adjectives, adverbs, and some conjunctions). The articles the, a, and an are always lowercase in a headline-style title, as are the conjunctions and, but, for, or, and nor.
The sentence-style title reads like this:
Mneumonics that work are better than rules that do not
Singing while you work
A little learning is a dangerous thing
The editor as anonymous assistant
In sentence-style capitalization only the first word in a title, the first word in a subtitle, and any proper names are capitalized.
The Chicago Manual of Style 16th ed. - page 448 - sections 8.155-8.156 - Capitalization, Punctuation, and Italics
Both of these styles are perfectly correct and standard. As noted in the question, editing titles on a post can cause the question to go through the feed again for some users, so I think changing the title of a question should be reserved for bona fide errors and not tinkered with for stylistic preference. For users who can approve suggested title edits, it's important to make sure there is actually something wrong with the original title before automatically approving another person's suggested style changes.
If all spelling, grammar, and punctuation in a poster's title are correct, the OP's style preference -- headline or sentence style -- should be respected.