Reviewers who are trying to assess a paper's contribution tend to get annoyed when that contribution is exaggerated or, worse, is a reinvention of prior work. A corollary to this comment, is that the authors should make the readers aware of the limitations of the work in the paper. Doing so typically strengthens rather than weakens the paper. Because the program committee usually does not have any way to ensure that the authors will revise their paper to fairly assess the shortcomings of the work, they will typically err on the side of caution and reject submissions that fail to do so. Keep Within the Page Limits .
Reviewers have to do a lot of reading.
Overlength papers do not win friends. But Be Complete Sometimes authors, struggling to stay within page limits, leave out crucial details. A classic example is the paper that omits some proofs for brevity. Don't leave out a critical detail. Find a way to fit it into the paper.