Even though there is some kind of information available on this topic, I just would like to add a different perspective to this point. The first and foremost point is that SAP has had different currency types from the beginning days and SAP keeps improving the feasibility based on the global requirement. Just I tried to differentiate between SEP ERP & SAP S/4HANA about Controlling Currency Type.
In the SAP ERP
In the SAP ERP system, you had the option of having 3 currency types in the FI module for each company code, 2 currency types in the CO module.
In ERP, we used to Maintain 10 or 20 as a Controlling Area currency type. As per my knowledge, I have seen in all my implementation we used to maintain 10 or 20 Controlling Area currency. Moreover, Material Ledger is not mandatory during ERP days,
In SAP S/4HANA
In SAP S/4HANA, it allows the addition of eight extra user-defined currency types. When added to the company code currency and the global (controlling area) currency, this means that there are now 10 available currency fields in FI.
Note that even though you now have up to 10 fields available in the Universal Journal, that doesn’t mean you need to use all of them. In fact, many companies will use only two of the currency types-local and global.
But In S/4 HANA, SAP has suggested maintaining Controlling Area currency type “30” as per Note: 119428.
What is the basic reason for this currency type setting?
Currency type 20 is only known by cost accounting, whereas currency type 30 is known generally in financial accounting, Therefore, data transmission via the modules CO, AM, and FI works without any difficulties if type 30 is used by all.
Moreover, if any client needs to work with parallel valuation approaches then Currency type ’10’ or ’30’ has to be set in the controlling area (other currency types are not supported in this case).
Does Controlling Area Currency Type “30” works in S4 HANA?
So the bottom line is that it would be safe to use currency type 30 in the controlling area
Raja Sekhar Andey