Backlinking the Backlinks...

It seems to me that generally I get the idea that people use bookmarks, forum profile spam and blog comment spam by the heap to backlink their better links pointing to their money sites such as Web 2's, articles, videos and so on.

My questions:
Is this spamming done just to get these better links indexed?
Can you replace all this work with adding a service like lindexed to get the better links crawled and hopefully indexed?

Thanks for any insights...

Doing those things helps get them indexed but more importantly, it helps increase the authority of those better links in the eyes of google. This in turn helps increase the link juice that they are passing to your site.

Using a service link lindexed or linklicious would help get them indexed faster but it wouldn't help increase the link juice that they are passing on to your site.

Building low quality links to more low quality links is a complete waste of time in terms of ranking.

Yes, if you send backlinks to your backlinks it will help to index those backlinks but more important is that those backlinks will be stronger.

I have tried such scenario in the past and believe me its just waste of time and resources. It might give you a little benefit but it will be so small (almost negligible).