You do not always need to get links from related sites (in your niche, subject area) to rank better in Google.
I’ve engineered better rankings for sites getting links from unrelated sites so I would say getting links from unrelated sites is not a bad thing in itself.
It really depends on the sites in question, what you’re linking to, and the intent.
It’s a bit of a band-aid though. I’ve only used that method for clients who seem incapable or unwilling to add content to their site and to be honest I am moving away from those kind of clients all the time.
For maximum impact, it’s far more important to try and aim for links from related pages at least – ie a page with a good page title etc with your desired keywords in it.
A link on a page on an unrelated website with a measure of domain trust / authority discussing your subject area is worth it’s weight in Gold. I’ve actually increased rankings from unrelated pages too, though.
I am not saying don’t get links from related sites – the audience and traffic possibilities alone make links from related sites worth it. I’m just saying links from unrelated sites work just as well sometimes.
The same goes for linking to unrelated sites.
And I’m not advising getting links from unrelated sites or to use this strategy as the only linkbuilding strategy you employ, in case I upset the white hat shock troops.
I just think a link from any real site is a decent link.
It’s easy for seo to advise “get links from related sites….” – it’s safe, it’s what Google wants to see, it seems to compliment some of Google’s ranking algorithms – that’s why they do it.
Just don’t discount links from unrelated sites as useless – they are clearly not.