How many levels of Active/Active/(Active) have you seen. And what type of questions do you usually ask when designing these.

I've been performing a lot of Data Center installs here lately and admidetly ACI, but this probably applies to any cloud/SDN platform. As I am building out 3rd and 4th data centers I'm wondering, is Active,Active,Active,Active a thing or is there a practivcal methodology to scaling large scale multi region datacenters. Anyone have any good reading on the how many sites should be active vs passive and pro's and cons?