If you're still conscious after the event, your first reflex should be to take the dashcam off and hide it - unless you think there's more to record (like if more events are unfolding in front or at the rear of the car).
Law enforcement officers (LEO) can't force you to have a camera, but they can require the footage should they see that you have one.
Same for the adverse party.
You can always provide the footage later, if it plays to your advantage.
As for who's at fault - as long as your vehicle is moving (and sometimes even when it's not) - some percentage of blame will be applied to you.
The footage is not there to show how guilty the other party is - it's mostly there to show how perfect you are, and to dispute the false statements the other party will inevitably submit.
Never start the conversation - if any - with the other party with "I have a dashcam, you're so done". Be courteous and polite, start with "are you OK ?", give them a first name to call you by. Establish the facts, share them with the LEO for the accident report, de-escalate any possible tension while waiting for the LEO, then bide your time as the other party self-righteously sinks in their lies. If possible, have them sign on those lies. Then conclude with "I respectfully disagree, this is absolutely not how it happened, and I am confident my dashcam footage will confirm it".
As with any weapon - dashcam footage is to be used fast, by surprise, when it's needed, if it's needed.