Never walk into a meeting in which you have a relevant role – people expect you to present, to coordinate, to moderate, to organise -, without some careful preparation.
When you don’t prepare, you will either be talking too much or too little, the audience will get bored, the conversation will get all over the place, arguments will be shallow and discussions pointless. And there’s not going to be any concrete outcome. If you are not prepared for a meeting in which you have a relevant role, just cancel it.
This is also a great way to keep the numbers of meetings to a minimum. None of us is paid to prepare for meetings.