My memory isn't that good and I don't remember exactly how the whole idea of guest accounts started on Steem.
They are not exactly new on the internet and applied very well to the situation on Steem, where creating an account wasn't really free (even the 'free' ones had a cost in resources).
Few people are willing to pay for access to a platform they don't know and haven't been able to test-drive themselves. Thus, a guest account would be very useful for them to determine if they are interested or not.
A while ago I saw an announcement (or was it just a comment? Argh, my memory again...) that TokenBB supports guest accounts. Anyway, @reggaemuffin mentioned it again today in a comment, which makes it as "official" as it can be. At the time I thought: Cool, we really need this!
Now SteemPress implemented guest accounts as well. In a post where @Fredrikaa and @Howo presented their "biggest set of updates to be launched in one go", guest accounts were the central point, and with good reason!
Let's remember that while most projects on Steem are designed to work for the Steem community and eventually whoever else discovers or is brought to the project, SteemPress works the other way around.
It "goes" outside of our ecosystem and resides on the Wordpress blogs of content creators as a widget. And their audience keep seeing "Steem" at all steps when they engage in the comments section.
I think guest accounts are mainly about convenience and allowing free (but limited) access. I have a question, in light of freedom of speech and someone attempting to test the limit of that using a guest account. What would you guys at @steempress do if something like that happens and the guest isn't blacklisted by the author? It will be your account on which the comments will be made, even though it will clearly be formatted as a guest comment. Or should you create a separate account for that, and delegate enough RCs for operations? You need to think about that and make it clear what are the rules.
One more thing I believe would help improve guest accounts via SteemPress.
I think a Discover More Blogs Which Use Steem functionality would be useful for both guests (who can comment -- and potentially earn -- on more blogs) and authors. And this functionality would list a number of other blogs that use the widget. There should be an opt-out option too, in case someone doesn't want to be listed, for whatever reason. This could be improved, but would require more information, to only show related blogs.
Oh well, the more time I think about it, the more ideas come to my mind. But ideas are often not what we lack.
About a week ago we talked about light Steem accounts and how they can help improve onboarding. Light accounts need to be defined at the Steem blockchain level, if they are considered useful (and I saw Steemit talking about them too in a post about onboarding where they asked for feedback), while guest accounts can be implemented in various ways by any Steem project. They both would help onboarding in my opinion, because they can work together and aim at the same goal.