'Account Transaction' is optional on the Create External Transaction form in Cash Management?

The ‘Account Transaction’ option on the Create External Transaction form in Cash Management appears to allow the creation of unaccounted External Transactions — these can be used to reconcile bank statements but are not accounted for or recorded in the General Ledger in Oracle Fusion.

Is there any specific reason why this field is kept optional instead of being made mandatory? Kindly advice and provide any available documentation relevant to this.

Screenshot below for reference.

Thanks,
S Murali Mohan.