Compared to the desktop version, there are some limitations, such as the lack of components etc… but it is still an excellent solution for creating static sites.
Yes, this is a WordPress plugin, so yes, you must have a site, online, with WordPress installed.
You misread me So I rephrase, compared to the desktop version, the plugin brings in addition the possibility to create static sites from anywhere, any system that you own or not, without the need to have your PC or Mac available.
For the rest, it lacks some of the advanced features of the desktop version such as components among others.