Are there any benefits to using PF motors instead of EV3 ones? Can someone explain to me the key differences between PF motors and EV3 ones? I understand that EV3 motors are 'regulated', presumably meaning that you can control their rotational speed depending on the wheels attached and so on, but apart from that, is there any reason to use PF motors instead (e.g., XL ones)?

One reason why this question comes up is I saw lots of non-EV3 motors used with EV3s in a recent robotics competition I went to. Also, large wheels which you apparently cannot buy anymore (not from Lego, anyway).
The cost of a PF motor is about one third of an EV3 motor.
If there is no need to regulate the motor, using PF motors is a way to save costs. Also PF motors are more compact.
Its possible with lego converter cables to attach them to an EV3, however the NXT to 9V cable is hard to come by. Ofcourse there are DIY solutions (soldering) or third party components.