PM2 / forever if cluster is already enabled?

I already have cluster enabled in my application natively in node. I have decided to migrate to pm2 for production from the old node bin/www command.

Now, as we know, pm2 supports clustering without changing code. If I have clustering enabled natively, should I run PM2 in cluster mode as well or the default fork mode?

I'd love to know the 'why' behind it.

Thank you!

via QueSo