I'd say it depends on what type of site you are, how likely users are to click the back button vs. find the right tab, and how often users are clicking your (external, I assume) links.
One of the companies where I worked in-house had a link policy that all external links would indeed open only in new tabs. But this was for a corporate info site...so most of the links were to pages within the site.
You could argue that it's more likely someone will be directed away from your site if they have to hit the back button. They could get distracted by the new page and forget about yours. With a tab, at least your site sits there, making it easy for users to come back to it.
External links opening in new tabs of course becomes annoying only when a large percentage of all your clicked links are actually external - like a blog. But even in that case, what actual percentage during a visit is being clicked? If it's small, then it matters less. Also I know that for the most part, people skim instead of read, so they will click to "read later" while they skim instead of clicking to get absorbed. That means they'd want to easily navigate back to the actual article they were skimming before. Those are several assumptions there though. There's gotta be research on this, no?
A primarily-mobile site should probably employ minimal use of new tabs - switching between separate pages on a phone isn't as easy as on bigger screen browsers and can feel more like a popup.