An important part of any SEO campaign is to ensure that your backlinks are known to Google and the other search engines. Not all known URLs are indexed, in fact the vast majority of content on the Internet is not indexed. To ensure that your backlinks have some value it is best to have them indexed as these pages will undoubtedly carry more weight than an unindexed page.
Web pages that have links pointing to them will be known to Google as they crawl links on page and build the spider web. Linked pages will have a better chance of being indexed after being crawled a few times.
Better content on better sites will be crawled more frequently and will have a better opportunity of being indexed in the Search Engine Results.
Every niche is catered for on the Internet. Here are some examples:
cars and other vehicles;
camping and caravanning;