This step is necessary only in cases where your currency is not with two decimal places. Every currency with 2 decimal places is not necessary to be maintained here.
IMG Path: SAP NetWeaver -> General Settings -> Currencies -> Set Decimal Places for Currencies
After opening of the transaction you will get consequence of warning messages.
First screen warning message.
Second warning message.
Third warning message that you should read carefully before proceeding.
Currencies with other than 2 decimal places.
Here is the screen for New Entries maintaining Decimal Places for currencies with other than two decimal places.