That being said, Google's John Mueller took it a step up by saying using these services may hurt your rankings.
In a Google Webmaster Help thread John responded to a webmaster who was asking "mass website submissions to search engines," and asked if it will have any impact on their rankings.
John from Google said, yes, it may, it may have a negative impact. Why? John explained that it can lead to a tremendous number of unnatural links for your site. As you know, unnatural links can more than ever have a negative impact on your site. Despite the concerns with negative SEO, this is the reality we live in these days.
So yea, it sounds like in some cases you can use these services to negatively impact your competitors, assuming their link profile looks horrible anyway?
John wrote: These services are not needed and can even be counter-productive (if they create unnatural links for your site, which would be against our Webmaster Guidelines).
