What features will I lose if I disable Bonjour's 'whats-my-name' service? Upgrading to Yosemite (from Mavericks) enabled Bonjour's "whats-my-name" service on my Mac; I would like to disable this (for security policy reasons) but wonder if some feature (perhaps something new with Yosemite) will be lost if I do so.

What, if any, features will I lose if I disable Bonjour's "whats-my-name" service?
You will lose the visibility of your services on other computers (i.e. Finder sidebar). If you don't have any sharing services running than it is of no consequence and would be equivalent of a firewall not allowing multicast traffic from your Mac.

Because you did not completly disable Bonjour you will still benefit from seeing others on the network and cloaking of the ".local" domain in DNS. AirDrop, Handoff and Continuity all use BLE as discovery mechanism, not Bonjour so would not be affected.