Some people buy domains and park them for later use. Lets say you want to build a website later on a domain you buy today. While you are waiting to develop the domain it can be beneficial to park it.

One, to make money off it in the meantime, another to introduce it to Google's page rank system. While it is parked it should gain and retain pagerank within our system.

Another reason is to introduce it to all the search engines, get some listings and be one step ahead of the game when you decide to construct it.

More: Until You Want To Sell It