过而不改，是谓过矣 [A man who has committed a mistake and doesn't correct it, is committing another mistake.] (孔夫子 [Confucius], “論語 [Analects]“)

Nobody, least of all referees, enjoys a paper which is badly written and full of errors.

Even if the result itself is first-class, a cavalier attitude to expository or accuracy issues (or the presumption that it is solely up to the editor and referee, rather than the author, to address these issues) will negatively impact both the referee reports on the paper, and the editor’s final decision on the paper.

In particular, having an error discovered after the submission process, which then necessitates sending a revised version onward to the referee, tends to tie up a lot of time and thus slow down an already sluggish process.

Investing some time before submission to try to eradicate these sorts of problems (and to give the paper one last polish, in the meantime) is usually well worth it; it earns the goodwill of the editor and referee, thus speeding up the published process, and also improves the final product.

See also “Submit a final draft, not a first draft“.