Depends.
Anything that you are adding water to, like oatmeal, pasta, rice etc. weigh it before. The absorbed water will add weight and it will not be accurate. For meats, you'll get mixed responses. I would say choose one method and stick with it. I weigh my meats cooked. I do this because it is easier to meal prep that way, in my opinion. I can cook up a week's worth of meat and just take out however many grams or ounces I need.
Also, if one cooks meat, it loses retained water. That is also why I choose to weigh it cooked.