Hi,
A bit of searching will work wonders, this post answering your question is on the same forum page that you posted on.
Recommended Settings for the Security Audit Log (SM19 / SM20)
In terms of performance, as others have said, the performance impact will be based on:
What you are logging
Number of active users in relation to the above
Hardware sizing
Any ABAP system that is noticeably degraded due to logging will have far greater performance problems during peak activities in BAU.
On the MDM side I have only seen problems when there are sizing problems. Logging is a basic IT General Control so I would expect the requirement for it to be covered in any sizing activity.