Sip.conf defn: in-bound & out-bound vs out-bound only

Lets say I have a SIP provider which allows both in-bound and out-bound calls. How peer definition in sip.conf (or sip_additional.conf) for one and the same provider would be different if I want configure my asterisk for this provider for

  1. out-bound calls only
  2. both out-bound and in-bound calls

Do I at all need a registration declaration (register string) for strictly out-bound calls?

As I understand, for strictly out-bound calls, I do not need any USER Context/USER Details record.

Let me draw an analogy with Sipura 3000 settings on Line 1 tab. In order to make both in-bound and out-bound calls, I can put the provider to “Proxy and Registration/Subscriber Information”. Whereas in order to make out-bound only calls, I could put the provider to one of the Gateway Accounts. How this would translate to asterisk settings in sip.conf (or sip_additional.conf)?

(Cross posted in voxilla forum)