That is probably true, however, I personally use it to share with others who are not part of my network, calendar integration, password database access across many devices, rsync backups across baby devices, document editing via collabora and probably other things I’m not thinking about at the moment. I don’t have the performance issues that others note, but I took all of the performance improvement steps noted in the documentation: have bare metal well-resourced db hosts (for multiple services), dedicated redis cache, properly configured php-fpm, etc.