Which record are you asking about?
The _sip records are an option for implementing resiliency/failover to the SIP PUBLISH trunk from CUCM. In the past they were also used when leveraging CUPS (now IM&P) as a SIP Proxy, such as with UCCE. That reference design has moved to CUSP though.
The _xmpp-client and _xmpp-server are useful for 3rd-party / standards compliant XMPP clients or servers, respectively. For example, _xmpp-server must exist on the public DNS zone, pointed at Expressway-E for inter-domain federation.
