The downside is you can only share to other users on your Vaultwarden instance. You can't e.g., set up emergency sharing to family members who use cloud Bitwarden.
BW clients support having several accounts at once so you're not forced to choose. Your family can have a regular bitwarden.com account and your vw.example.com account just for emergency access
No idea how this maps into Bitwarden's own offerings though but all clients support this kind of thing