It doesn't really require an always-on-system. That depends a little bit on what you use it for.
For example I use it to synchronize the photos from my phone to my Laptop, whenever they can reach it other either by being on the same network or by connecting to the global syncthing "introducer" system, they start syncing.
Having a "cloud" system becomes useful if you need to share a file with someone who's not online with you at the same time, which is a pretty big use-case I supposed. But that is a problem that any alternative that is software only will need to solve via some service.
Nextcloud for example or also Seafile. Both have nice clients, but require some sort of server, whereas with syncthing the cloud part is optional.
For example I use it to synchronize the photos from my phone to my Laptop, whenever they can reach it other either by being on the same network or by connecting to the global syncthing "introducer" system, they start syncing.
Having a "cloud" system becomes useful if you need to share a file with someone who's not online with you at the same time, which is a pretty big use-case I supposed. But that is a problem that any alternative that is software only will need to solve via some service.
Nextcloud for example or also Seafile. Both have nice clients, but require some sort of server, whereas with syncthing the cloud part is optional.