If you run a production SAS environment or even a development environment for that matter, it is nice to have a specific location for all logs to be written and managed. ALTLOG helps achieve this.
The ALTLOG option can be set numerous ways, but we typically utilize 2.
1. As an option on the command line. Example:
sas sasprogram -altlog /my/log/dir/sasprogram_$timstamp\.log
2. Globally in the sas configuration file. This is wonderful as an administrator. All of the logs drop into one location for easy cleanup or archival. Users can specify an alternate location if they don't want it in the default, so everyone wins.