rsau/enable is a SAP Parameter attribute which is used to control Enable Security Audit information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
0 audit not activated
1 audit activated
Caution
Audit is only active if you used Transaction SM19 to maintain and
activate a corresponding audit profile. You must also specify the
directory, name, and maximum size of the audit files using profile
parameters.
Depending on the settings, audit can lead to large audit files.
Ensure that there is sufficent memory in the file system.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.