Usually sparring is just to simulate the style of the opponent. However, if you are hired to be the sparring partner to simulate the punching power of the upcoming opponent, perhaps you shouldn't hold back.
If you are being brought in for a proffesionl training camp and are being paid, then yes you give it all you got. Roach will pay a sparring partner an extra 1k if they drop pacquiao in sparring for example.
Controlled sparring for developing skills. Full contact sparring you go full speed ahead. Some fighters just go full contact(Margarito), others mostly just controlled, and some both. I think you need both. You won't improve or learn more if its just full contact.
Some sparring sessions turn into heated battles.Sometimes the main actor gets an ass whopping.See Hatton vs Lara.
Yes and no. Sparring partners have specific roles and are instructed to fight in a style that might not be there natural style. So while they are giving it their all, they are also limited as to what they can do. A sparring partner trying to imitate Malignaggi for Cano's next fight isn't going to go in there and throw an overhand bomb- even if it's his best punch in his own fights.
Nope they are not allowed and as soon as they make the company fighter look bad they get fired and replaced. :hat