You can also customize the look and feel which I've done to match my branding and logos/colors. Too much customization might be difficult to maintain through the various upgrades as they overwrite files but as long as you know which files you've changed to customize, you're all set.
I have made my Nextcloud instance available to clients to allow them to share large files with their customers/clients instead of using email. I've set it up so that individuals from only a subset of domains can self-register on the server which allows them to share files. For example, only users of domaina.com and domainb.com can self-register while everyone else gets a "sorry but you don't match the allowed domains" message. This means I don't have to manage registration each time.