From the In Nomine site run by Steve Jackson Games:

Only a step below the Seraphim in divinity, the Cherubim have always been much more active on Earth, protecting all God's creations. No Choir works harder (only the Malakim are their equals in relentless devotion to duty). If humans knew just how much the Cherubim have done for them, they would occupy the most privileged station in angelic lore.

"Thou shalt not be afraid of the terror by night, nor the arrows that flieth by day, for He will give His angels charge over thee."
- Psalm 91

Stout-hearted and strong-willed, the Cherubim are the most generally reliable and fanatically loyal of the Heavenly Choirs. If the Seraphim are the nobility, then the Cherubim are the knights in shining armor, guardians of things held dear.

Their relation to the Symphony is one of ultimate devotion - with a touch, they can attune themselves to something (or someone), and as long as it exists on the corporeal plane, its perceptive protector will have a general feel for its location and condition. If it is destroyed, or in immediate mortal danger, he will know instantly.

This sort of simple-mindedness is the most basic expression of their nature: constant and solid, aware and vigilant....

For a Cherub, betrayal of devotion is the most serious sin, and generates dissonance. As long as he is attuned to something, he is its caretaker - its guardian angel - and won't do anything that would bring it harm....

But even aside from applied resonance, a Cherub must never betray his Superior, his friends, his ideals, or himself. Doing so would be to sink below his capacity for nobility, the first step down a short road to selfish malevolence. For this reason they struggle (sometimes in vain) not to divide their loyalties.

Cherubim move slowly but with severe purpose, their bright eyes missing no detail of their surroundings.... In their celestial forms, Cherubim look like enormous, winged animals - lions, bears, etc. - suffused with haloes. Why Western artists began depicting them as cute, pudgy, winged babies several centuries ago remains a mystery. The Cherubim were not amused; most suspect the Diabolical's influence.

As the ultimate celestial protectors, Cherubim are the best angels to have guarding your back - and although a Cherub may say he needs no protection, the best angels of the other Choirs, led by the Cherubic example, make it a point to look after them anyway.