In the control panel, when you rebuild member stats, you also rebuild the calendar birthday list. I guess Gizzy means that unless you choose to rebuild member stats (it doesn't do it on its own, only when you either upgrade the board or specifically tell it to rebuild), it shouldn't make your board any slower.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.