Muggles' Guide to Harry Potter/Magic/Petrificus Totalus

Overview
Petrificus Totalus is a spell that freezes or petrifies the body of the victim, making it incapable of moving, except for the eyes and breathing. It is also known as the Body-Bind Curse or the Full Body-Bind, the latter being used apparently to differentiate it from Locomotor Mortis, the leg-locker curse. The spell can be broken by the Finite Incantatem spell.

Extended Description
This is apparently a fairly simple spell, as Hermione uses it on Neville late in the first book.

Harry will use this spell himself on a number of occasions. Perhaps interestingly, it is almost exclusively used against Dolohov, who is twice petrified by Harry in the battle at the Ministry of Magic in Harry Potter and the Order of the Phoenix, and at the top of the Astronomy Tower in Harry Potter and the Half-Blood Prince, then by Hermione in the all-night cafe in the Tottenham Court Road, and finally by Parvati Patil in the climactic final battle in Harry Potter and the Deathly Hallows.

It will be used by others on Harry as well; notably, in Harry Potter and the Half-Blood Prince, Draco Malfoy will petrify Harry and break his nose, and later in the same book, Professor Dumbledore will petrify Harry to keep him out of the action and safe. Once Dumbledore is killed, the curse wears off on Harry.

Analysis
The Harry Potter story arc, consisting as it does of an epic struggle between good and evil, will have fights, larger battles, and perhaps even an all-out war. In order to prevent the series, ostensibly for children, from becoming excessively dark, there must be non-lethal weapons for the protagonists to use. To that end, the author has provided us with a number of disabling spells, ranging from the simple stunning, disarmament, and binding jinxes, through to those with humorous effects. It is uncertain why there would need to be so many different ways to disable, but we can surmise that the author has at least some reason for use of each variety. Notably, the full body-bind jinx here leaves the subject fully aware of what is happening, able to see and recall what proceeds around him after he has been jinxed.

Greater Picture
It is mentioned above that a person disabled by means of this jinx retains his sight and the ability to observe and recall events occurring around him. Apparently this knowledge of the passing scene on Dolohov's part is what alerts Voldemort to Harry's escape from Death Eaters in the Tottenham Court Road coffee house, after his departure from The Burrow in Harry Potter and the Deathly Hallows. Voldemort would not, otherwise, have any reason to punish Rowle for allowing that escape. As such, it is a useful plot point; knowing that Harry is no longer at any of the Order of the Phoenix safe-houses, Voldemort is likely to hold off on further torture of occupants of those houses, including Ron's family.