David Harry: When it comes to guest blogging, or any form of link building, it's not as much about the tactic as it is the location. ;
Would I want a bunch of guest blogging posts on crap sites? Nope. Would I want to post on a top authority site (like Search Engine Land for the SEO world)? Yer damned right. ;
Forget about the links and start to consider the source. Even if the links are nofollowed, would I want my client to be on the site? That's the real question. The goal at the end of the day is to bring attention to the client and get people to follow them on social, to go to the site and the site's blog etc... If you're producing compelling content, the rest will take care of itself.
Jelani Burton: I agree with +David Harry, guest blogging can still be leverage to improve SEO but it can also have negative effects. ;G can sniff out paid/sponsored guest posts so you need to be careful where you blog.