Oftentimes people want their carpets smelling fresh and the truly green people want something that is also earth-friendly.
This idea was borne out of the fact I wanted to deodorize my carpet and I bought some Arm & Hammer scented carpet deodorizer. My was it potent. I it made me sick (yes, I made sure to vacuum thoroughly. Not only did the properties of it make me sick, it didn't so much as deodorize, as "poison" the airspace so greatly I ended up having complications to my asthma.
I know I want my house smelling clean, using a green product, without having an asthma attack.
You would obviously vacuum it up so you don't want to make it seriously biodegradable, but for people with vacuums that suck (literally and figuratively) it won't harm anyone, even pets (if your pet eats something off the carpet they won't get poisoned if there is any leftover residue).