Thunderbird vs Thunderbird Portable

I've migrated my email from a copy of Thunderbird on my hard drive to a copy of ThunderbirdPortable on my USB hard drive.

This installation does not seem to adapt to junk. I have to manually mark messages as junk, and it just doesn't seem to mark on it's own.

This issue has gotten me thinking about ThunderbirdPortable in the larger context. What exactly is the benefit of using ThunderbirdPortable over a local copy of Thunderbird that would reside on my USB hard drive? What are the changes made by the default portable configuration and can they be undone? Are the changes in the Thunderbird profile or made by the launcher?

Thanks for any info...

Jim