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LOGPARM allows LOG and altlog to have dynamic name
history and purpose the LOGPARM option was introduced (perhaps) to support SAS server logs, which became large as such a server might run for a very long time and might overflow the capacity of the drives to which they write.
Alternatively there might have been other reasons for establishing this feature.
Although this link describes the role and relevance for Non-Interactive SAS LOGs (aka batch mode), when using Interactive SAS (aka Display Manager or DM) where there is no log file because LOG is directed to a window, the same LOGPARM features can apply to the ALTLOG file. LOGPARM supports Interactive SAS