No idea what to put as a title
There are two types of deportee's, escorted (DEPA on the manifest) and unescorted (DEPU). As rightly said the escorted are those who need to be baby sat because they can kick off in flight. They could be people who have sent time in jail in the UK and then being sent back to their home country. They used to have only two escortees with them but they have upped them to something like 3 or 5 regardless of what crime or how much they are acting up. It's just the company who looks after the deportee's SOPs. If the deportee is acting up and kicking off they will tale them back to the cells and try again later. If they act up on the aircraft the captain tends to say no get them off. It upsets the paying passengers.
The unescorted on easyjet tend to be visa refusal but they are still detained by the same company as above and brought out to the aircraft under guard who will leave them and leave the aircraft once they have sat them down and hang around until the aircraft pushs back.