Would you mind giving me examples of things that have occurred?
It enables people to form their own independent groups, which disturbs AI allocation by fragmenting player groups*. It also enables people to play roles they are not slotted as, which disturbs players when they slot in for that role, but find it is already being fulfilled. We saw a similar thing happen all the time when we had vehicle restrictions disabled, essentially someone would fly transport without being in the slot, and then someone would slot in as buffalo only to find someone already flying. These are things that several zeus's and other people in S3 have observed occurring often.
*essentially the server can support a finite amount of AI, and it only takes a single person to activate a spawn zone, so people going out and doing their own thing spreads the AI unacceptably thin