Your domain. It’s not just your reference on the web, it’s also your track record with Google. And most likely it’s been used by someone else. What if that someone else misused the domain? What if it was a SPAM site. I hear of so many site owners working really hard on their SEO and not getting anywhere. Most of them did not check the domain they payed for.
Why dose it matter?
Google has to deal with a lot of SPAM. You would not believe how many sites try to pull one over on the search engine. And having to re crawl them to see if they changed their ways is not worth the time. So they discard them, making sure they will not be indexed again.
When you but a domain you must make sure this is not the case with you. To do that you can use a website called way back machine. Just enter your domain and you can see if it has ever been used. And if so what has been done with it. Take a look at the content of the sites that have been hosted on your desired domain and you will have a good idea what has been done with it.
If the domain was used for SPAM you can still work really hard to get it back in the index, but it’s just not worth it.