In addition, the attorney's trial preparation materials, known as attorney work product, are, in general, not discoverable. Assertions of such exclusions, however, can be challenged. Information obtained through discovery is useful in determining what the other side's case is in the litigation. For instance, it is common for litigants in patent suits to engage expert witnesses to testify on technical issues. Discovery can be used to identify the experts, determine their qualifications, review any tests performed by them and scrutinize their theories and conclusions.
Discovery is also useful in committing the other side to a set of facts.
If facts presented at the trial differ from the sworn answers to interrogatories or testimony given in depositions, the party's credibility is open to attack. For the most part, deposition testimony given by a party, or one who speaks for the party, may be used for any purpose at a later trial. Deposition testimony of a person who has since died or cannot be compelled to appear can also be used at the trial. Discovery as a means of gathering information in litigation is effective because there are sanctions for those who do not comply or abuse the process. The most serious sanction, dismissal of the suit or default in favor of the other side, is rarely applied.