OwnCloud/Nextcloud is a great application for cloud storage of files, and makes sharing specific files or folders easy and fast. It also makes a great tool for real-time collaboration, including real-time chat and simultaneous editing of documents or spreadsheets. I have used ownCloud to assist clients in sending large files that could not be emailed -- for example, one of my clients is a Video Production agency. They produced a commercial to air, but could not email the file as it was 400MB. OwncCloud came to the rescue. I set up a temporary share and allowed him access to upload into that folder. Once the file was in the folder, I generated a share link that was then forwarded to TV stations for instant viewing in a browser. Each TV station then downloaded it and was able to add it to their scheduling system quickly. From the Photography side... I am able to deliver large amounts of files quickly and easily to my clients, and they can download or view on mobile devices easily. Since I use ownCloud on a daily basis, I cannot think of any reason why I would not use this software
OwnCloud is easy for me to use, and I believe it would be for others too. The barrier for most people will be the set up. For a technology professional like myself, ownCloud's setup is pretty straightforward, but it's not the sort of thing most casual users will be able to handle. Also, it's on the user to maintain the service. These can be taken care of by paying someone to do it for you.
Compared with other cloud services, ownCloud has been the most efficient. It doesn't create a noticeable drain on resources and very quickly syncs across all my devices. I'm usually able to save a file on my laptop and by the time I walk over and sit down at my desktop machine, it's already there. I don't need to wait as often as I have with services like OneDrive.
Regarding the community edition, there is a reasonably good support on the IRC, forums and in the issue section on Github. Perhaps a much more individual approach would be available if the premium support was chosen and the instance of the server was provided by the Owncloud company that also offers some premium extensions, not available generally. However, we did not need this level of support yet.
ownCloud is better than Google Drive and Microsoft's OneDrive. I have not used Google Drive in some time now, so it may have improved. OneDrive has become better over time too, but my go-to is still ownCloud. Firstly, I prefer to have my data under my control. No other service can offer the level of control that ownCloud does. Setting that aside, in my experience Google Drive never quite got syncing right. Unless you have a very small collection of files and you're not synced across many devices, Google Drive fails to achieve a complete sync. The icon is always showing that Drive is syncing (and not up to date). I've had similar issues with OneDrive, but these days on Windows 10 OneDrive usually can achieve a complete sync across multiple devices, but it often hogs CPU and Network resources to do so, and it's still slower than OneDrive.
The company grew from 4 employees in 2013 when ownCloud was initially deployed to about 40 in 2017 and still using it with a very similar setting without any major upgrade on the same Linux VPS. 95% of all company data are stored and shared via ownCloud successfully. No clear data about ROI but clearly the perfect adoption rate by all people and its ubiquitous use makes it an essential part of the company workflow.