I see a lot of questions with titles like "limit question 4" or whatever. Should you number questions? It seems like a poor way of titling questions.
Titles like "limit question 4" appear because the site blocks the submission of a question, if a question with identical title already exists. Most likely, the author's intended title was "limit question". They were told they couldn't use that one; adding a number to the end seemed the easiest solution (and if 2 is already taken, just put 3, etc).
Nearly all of those questions are garbage; my Review+ extension uses "title ends with a number" among several heuristic methods to identify downvotable and closable questions.
But if it can be salvaged with an edit, great...
Daniel R.'s comment pertains to a quite different situation: including the number under which the problem appears in some textbook. It's commendable that someone cites their source properly; but the number belongs in the body of the question, not in the title. The title should give readers an idea of whether they would be interested in the question. A reader's thought process is unlikely to be "problem 6.14? No, I don't like that one... I would read if it was 6.26".
In such a case, I normally find a place for the problem number within the question body, and replace the title with something more descriptive.