Utilizing any feature of a product should be purely based on the requirement or it will just be overhead of an administrator. Surely there are difference between AH and SA repo. If you are a large enterprise and ePO is heavily loaded where ePO server is a bottleneck then AH is necessary. If AH is implemented then the assigned clients will connect AH for policy and to upload events. AH will then forward events to db directly. AH is nothing but a seconday ePO without console.
And large enterprises are considerd to be 200K systems and more.
Besides that, if you upgrade ePO, you will need to upgrade each AH to keep them working, so for each side a SADR require less maintenance.
ANd if I remember correctly, If you have 250+ nodes connecting to the AH, it is recommended to have a dedicated server running the AH software.