Questions may be asked of deponents that could not be asked of a witness at trial, because the rules are looser with regard to taking depositions. The deposition is a powerful tool for getting at the truth. It can also be misused. Depositions may be used in lieu of live testimony at trial in certain circumstances, e.g., when the deponent resides at great distance from the court, when the deponent dies before trial, and when the deponent later called as a witness at trial contradicts the testimony given at the earlier deposition. Since the court may sustain your opponent's objections if you attempt to depose a person more than once, it is wise to know as much as possible about your case and your opponent's position before taking depositions.
Some lawyers believe the taking of depositions is all that's needed before proceeding to trial.
In most cases, written discovery should be used to get a clear idea of the facts of the case before taking depositions. If a proposed deponent is leaving the court's jurisdiction or threatened with grave illness, prudence will depose such person as soon as practicable. In some cases the court may grant a party leave to depose such persons even before the case is filed. The court's order granting permission, of course, is obtained by making a timely motion . The legal proceedings at which a party acts to depose another party or third person by asking questions of such party or person under penalties of perjury.