A good servant can be worth a lot to a noble, especially if he is versatile and fiercely loyal, like Cosimo Melior is.
His family served the Lords and Ladies for generations and so he even was taught the skills to very effectively defend his liege if needed and he would die to do so.
The combat special ability protector (AC p111) allows a fighter to parry on behalf of a nearby combatant (at a -2 penalty).
For most fighters that don't use a shield, parry tends to be rather low. Using the Fedorino combat style special ability in combination with a defensive posture, dual hook daggers and the catch blade and cross-block special abilities gives Cusimo quite high chances to protect. And thanks to master parry, successive attempts in the same combat round only incurr a -2 penalty instead of the normal -3. In addition his noble master also forked out some nicely improved hook daggers, one even made with Toshkril.
This is for emergencies only and can be a nasty surprise for anyone bent on harming his master.
Cosimos main purpose is it however to organise his masters day to day life, including running the business (Commerce 12) and generally making sure his master 'looks good' in social encounters (Clothmaking 12, SA Craft Flamboyant Attire, Etiquette 13, SA Valet)
Due to his dedication (Obligation III) he has no real private life to note.