Jumpseater
Put simply I can monitor my pax more effectively from the back seat and have the ability to take them with me in a controlled fashion should the need arise.
In modern Hawks the front seat also gives a better ‘experience’ due to the avionics suite. I can control everything I need to from the back seat. The pax would need no specific extra training to occupy the front seat.
Remember this is just my personal (hopefully informed) opinion.
BV