What are the advantages of mutilating someone, rather than just killing them?

In Manhunt, I've just finished the tutorial level, where I am shown that, during a stealth kill, the longer I hold the action button for, the more gruesome the attack becomes.

Now, there are several disadvantages to this:

• Performing a fully-fledged mutilation takes a good 5-10 seconds, during which time the victim is likely to turn around, or I am likely to be spotted by another Hunter.
• The more gruesome the attack, the more noise it makes, so, if there is a Hunter with friends nearby, and I brutally murder him, they will hear and come to kill me.

So, I am left wondering: what is the incentive to brutally murder someone in this game?

The more brutal your kills, the higher your ranking at the end of a level. Reaching a 5-star rank requires you to achieve a set number of brutal executions.

Taken from the game's Wikipedia page:

At the end of each scene, the player is graded based on their performance, and awarded one to five stars. Unlockable content becomes available only when the player achieves three or more stars on a certain number of levels. On normal difficulty (called "Fetish"), the player can earn only four stars; one is awarded for completing the scene under a certain amount of time, and one to three stars are awarded based on the brutality of the executions carried out during the scene. On hard difficulty (called "Hardcore"), the player is graded out of five stars; one for speed, one to three for brutality and one for simply completing the scene. To gain the maximum number of stars, a set number of brutal executions must be carried out over the course of each scene; face-to-face fighting does not award stars. [original source, IGN]