Why might Exchange Rates need to be maintained at 1 in multi-currency?

Summary:

We use multi-currency but historically the exchange rates under General Site Options have always been set to 1 for each currency in our environment.
We would like to explore updating the exchange rates, but we are trying to understand the full impact.

Content (please ensure you mask any confidential information):

There is a note on Knowledge Article KB18645 (https://support.oracle.com/ic/builder/rt/customer_portal/live/webApps/customer-portal/?anchorId=&documentId=KB18645) saying that "In some cases, it may be appropriate to set this value to one."

Has anyone identified what scenarios might require this? I raised an SR with Oracle to ask, but they referred me to ask a question here.