You should pressure wash your deck for regular maintenance and before staining it, but do it carefully. Pressure washing is used to remove contaminants and embedded dirt. Avoid spraying too forcefully — this could damage the wood or composite and require expensive repairs. The softer the wood or material, the less pressure you should use to clean it with a pressure washer.
If you don’t know how to properly use a pressure washer, hire a professional to do it instead.