Well my answer is first off always NO. Thats a good starting point when dscussing when you should use a CAS or not. Simply the answer is NO NO NO ! There are a few exceptions but they are very few.
- Do you have more then 100 000 clients? Sure go for a CAS due to the supportability of 100 000 clients on a single primay !
- Political issues, if you loose go beat on the wall again untill you win.
- Building a Gloabl 24/7 organisation where you want to give your self time to work on the systems dusrint night etc might be one but not nessecary one depending on how you stand up your roles.
Almost all the old arguments for adding a primary are gone, two classical examples below.
- Delegation of duties haveing one group manageing the servers and another managing the clients, All that you now can manage with role based administration.
- Different Client Settings client in Sweden should have one setting and the German clients another, in SC12 CM now you can do Custom Client settings that you target to Collections so they are no longer site based.
As always when I do designs try to keep the hierachy as simple as possible, making it to advanced is also making it require more effort managing in most cases. Above is not all cases we will bump into but want I really want to get out here is dont just put up a CAS because you think you need one, you should have very valid reasons for standig up a CAS as it will addd more complexity to your environment. SC12 CM is really about hierachy simplification, I know it will take some time to get this out there but make amental note dont stand up a CAS just because someone said so.