At least with Henderson PD, the primary reason they do it is officer safety, not for liability/logging. For a barricaded situation they will move one patrol vehicle up fairly close & switch it's radio to a Tac channel & set it up so the Radio is re-broadcast through the vehicle’s PA system. Then someone using their hand held on that channel from a position of cover can make the announcements and have them be nice and loud at the house in question. If/when SWAT arrives with one of their Bearcats, often a SWAT officer or CNT member inside the Bearcat will try to talk to the suspects via the Bearcat's PA system. They do often have the dispatcher log when the verbal announcements have started and they do make sure that officers elsewhere on the perimeter can hear them as part of the documentation that the announcements are being made, but most of the time it's just the on-scene commander advising Control to log that, and that they can be heard by personnel doing rear containment.