This URL may help you get some answers to your question:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/cucos/8_0_1/cucos/iptpch6.html
You have certs for the web service and you would need to upload certs for LDAP (if doing secure LDAP). You may also have certs for encrypted call control/signaling and media (SRTP). If you had a TLS connection established with another call processing system (e.g. SIP trunk to a Cisco Video Communications Server, SIP to CUPS, etc.) then you would have additional certs loaded. Out of the box I have 17 certs on my lab CUCM 8.5 server and I haven't loaded any additional ones.
HTH.
Regards,
Bill