When should NTPd broadcast/broadcastclient be used instead of client/server or peer modes?

No, the broadcast client mode is not supported on most OSes. The broadcast and multicast modes are inherently less accurate and less secure (even with authentication) than the ordinary server/client mode and they are not as useful as they used to be.

If you're adamant about this, you can soldier on...

Linux OS supports broadcast/manycast/multicast, but it imposes a CPU overhead by the virtue of putting older Ethernet NIC and its interface in promiscuous mode (by reading in all packets including packets intended for other hosts).

MacOSX (now macos) can support multicast NTP, but no support is given for it. You can use the following command to enable it:

sudo route -nv add -net 228.0.0.4 -interface en0

Microsoft Windows Time service does not support multicast/broadcast on Windows 2000 Server , Windows Server 2016, Windows Server 2012 R2, Windows Server 2012, much less any of the Windows desktop variants. It used to support multicast NTP (K9 from www.mingham-smith.com/k9.htm provides multicast NTP for Windows 3.1, 95, 98, ME, NT, 2000, XP, 2003, Windows Mobile 2003).