All domain's host have the feature of parking a domain. Park a domain means that someone leave his/her custom domain for the burst of ads with having zero contents. You can think that is it better for you or not?.

Before launching the Google Panda and Penguin Updates, parked domains getting very traffic from search engine and causing trouble for the internet users. 

These type of domains have no content instead they are decorated with a lot of ads. These are usually Google ads and when a user click on any link, he get nothing but the parked domain owner succeeds in his aim.

There are many points at which parked domain are generating in a lot of numbers day by day.

Whenever you purchase a domain from any host (e.g GoDaddy.com) they offer you to park your domain for minor yearly charges. This is the case when you have bought a domain before launching your website (Mostly people purchase a domain name before launching a site for future reservation). So the people who do not know about the "Advantages" of parked domain, become the victim of this "feature". They think that instead of remaining free, it is better to earn some money from that domain. But they are killing the future of that domain. Because now Google is discouraging such sites by removing them from search engine list. And if, by chance a user gets access to that site, he may make a click on the ads (obviously), but when he finds nothing then that domain name will earn a negative point and that user will never come back to that domain directly or through search engine.

The other way if you do not park your domain then your host will make it "Parked Domain" without your permission if you leave it useless.

So if you purchase a domain, then also purchase web hosting and set a home page with some text or image to guide user about a bit future of that domain. This will cause to leave a good effect on the user and he may visit your site in future.

To secure the future of your site, parked domains are not good choice for you. So escape your domain from parking and leave a good effect on the user before launching that site.