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Once you know you've got everything you want out of them, you may as well drag them to the Trash. They're only there in case there's something not carried over automatically in an upgrade/rebuild.
 
After I upgraded to Tiger, I was paranoid about deleting my archive install "previous system" folder for a long time....lol

I tried burning it, didn't work

I tried backing it up to my external drive, nope...

finally I just trashed it, and there were no issues...

take the plunge...:)
 
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