Requests for admission ask a party to admit the truth of facts, the application of law to fact, or the genuineness of documents. Anything admitted is conclusively established for that case only.
The deadline bites. In most systems a request not answered within the prescribed period is deemed admitted. Courts have discretion to permit withdrawal where the merits would be served and the requesting party is not prejudiced, but relying on that discretion is a poor plan.
Denials must be honest and specific. A party may not deny for lack of information without stating that reasonable inquiry was made. A general denial of a request that is partly true is improper; the responder must admit the true part and qualify the rest.
Cost consequences. Where a party denies something later proved true, many rules allow recovery of the cost of proving it, including fees. That sanction is under-used and worth invoking.
Best use. Authenticating documents so that trial time is not spent on foundation. Establishing the undisputed spine of the chronology. Narrowing an opponent’s theories before summary judgment.
Worst use. Asking a party to admit the ultimate issue. It will be denied, and the request has told the opponent nothing except that you wanted it.