Best Practice for handling SUM log files

[su01]

Background:

During the upgrade SUM generates log files. From the SUM guide, help docs and experiences I've learned, that...

• SUM itself copies log files of past runs into a separate folder structure.
• There's also some advice from SAP to cleanse old log files.

Now I wonder what is the actual best practice? How are you doing it?

I would assume...

• the recently created or the older log files are taken off the fileshare and kept in a cheap storage location. Directly readable or in some compressed archive.
• the files are kept for longer as they document what happened. Because some issues / warnings or situations might have gone unnoticed but raise issues later.
• the files can help also in SAP support cases
• the files are never deleted for above reasons or only deleted after x years or n further upgrades,...

Of some I've heard they didn't care about them, some throw them away real quick, some zip them directly after to a separate fileshare... it's wild.

Question:
Once a technical upgrade is completed - do you keep the log files created by SUM? How long? How far of reach? 
Please feel encouraged to share your experiences even if it's already listed by someone else.

Thank you