Can someone please explain to me how important link injection is? Do I literally create a PBN domain about it's previous topic let's say dogs (titles - metas - alts)? Then have an article that has to do with dogs AND my money site niche (could be phones) in order to link it up? So I would write an article where theres a gps device on phones to locate your dog. So my final question is, is link injection essential and why do people do it? Is it to be natural OR it gives more juice?