Nextcloud is open source - there is no legal limit to your use of Nextcloud. We simply warn users of large installations that if they rely on Nextcloud, they should consider getting a subscription to ensure they have a solution that is enterprise-grade. Without subscription you’re using a home user solution which is fine until it breaks.
Among other things, a subscription gives support, yes - I often call it “job insurance for the sysadmin”, as often your job is on the line if you can’t fix a problem in software that your company relies on. Your boss will ask you “why did you deploy random software from the internet instead of a solution from a vendor we have a contract with”
It’s not just someone you can ask “how do I share a file”, but you get direct access to our engineers who develop Nextcloud. We don’t have a ‘support team’ which asks if you’ve tried to reboot your server
It also gives you access to security information and security patches ahead of release, so if security is important for your company - you should get a subscription.
You also get access to portal.nextcloud.com which gives you a few pieces of software from partners, free or for pay. For example the Outlook add-in, which costs money, but we offer a free Nextcloud FileMaker Pro addon there as well. It also gives you access to documentation that we don’t have in public. That includes deployment advice, or specifc things like for the GDPR, for example, if you get a data request, you need our docs to comply.
We give training, do security reviews for customers who want that and we of course can do custom development. If you need something, you are being listened to - you’re a customer after all.