Some folks think that they may be able to spam their backlinks and elude detection by blending in with a “Natural” profile. Google doesn’t care how many backlinks you create for yourself, as long as those backlinks are meritorious. What they don’t want to see is backlinks that are pure spam. They work hard to detect that type of spam and they are going to treat it the same regardless of how your profile looks.
I personally believe they are laboring under the false notion that Google doesn’t mind spam as long as it created slowly or mixed in with some meritorious links. The problem with this notion is that Google looks for pages that contain spam and they devalue the links on that page by zeroing the page’s TrustRank which weights the value of outbound links. Most of the places that you place your spam will be found by other spammers and no matter how little or how slowly it is created those other spammers tend to draw attention to those pages, which results in the devaluing of your spam. A backlink profile, no matter how “natural” you think it appears, will not prevent this devaluing.
Eventually, most spammers figure this out and realize that the only way to get any huge benefit from spamming is to spam as much and as fast as possible to exploit that brief window between the placing of spam and the detection of spam.