Why would I have to purchase more storage?

why would I have to purchase more zoho storage? I can create more than one account for personal use each with its own standard storage size... and I can (but don't yet understand) unify all them in a group and administrate it. (if for someone email address aliases is a lack of normal zoho account; I have to think that portal offers much more) Help? ps: I didn't find a forum section about general account issues. Is it true that cloud storage is applied to all suite app of zoho ?!