I helped a friend build their site on Squarespace. Not impressed at all, all the themes are very similar in style, and you are very limited to what custom functionality you can add. I couldn't even display the most recent, say, 3 blog posts across the site in the sidebar, for example, which is a pretty basic function to implement. It's basically static content on every page.
For someone with zero web skills - or even common sense, it's not that hard to get hosting, install Wordpress and select a theme - it does the job. Any more than that and I'd steer clear.
I actually used it originally a few years back, not long after it first launched, and recall preferring it much more then than now, almost like they've gone backwards in its functionality. I guess when you try to cater for the lowest common denominator in terms of tech skills, that happens.
Dave is right, there are limitations. If you want fully customisable - you're better off with Wordpress.
However, you can create a functioning site in the fraction of the time a WordPress site takes. You can turn on developer mode and customise code though. We use them all the time for simple websites that don't need anything other than forms that work, and content that works. You can create really great looking sites quickly and easily.
I've used squarespace for a couple of things. It's true that they really limit your options in a lot of cases but if you dont need much customization it works great. The support team is pretty incredible too.
I always recommend Squarespace whenever a friend or acquaintance mentions they want a website.
Most of the time it meets their basic needs and looks fantastic out of the box on all devices so why not? The drag and drop features take a bit to get used to but if you've never touched code it is a lot easier to build a site yourself than try and work out WordPress and Plugins.
The ability to add galleries as lightbox or carousel anywhere on a page and have it work perfectly first time is an example of the ease of use Squarespace provide to the non tech heads.
I like to have full control myself of my WordPress themes and features but I think it's important to know how these drag and drop site builders work as they're only going to get more popular and there will be paying customers out there asking for help to setup, tweak and enhance these sites.