Updating Sandbox

[DaleMeyn]

I apologize for typing "Copy - all files" instead of "Backup - all files". It's hard for me to keep all those scripts precisely stated when trying to type the message and juggle 2 other windows simultaneously. I haven't lived with them long enough to have them all memorized.
Page 41 of the User's Guide does not address updating the original volume from Sandbox, rather, it explains how to do a Smart Update from the original volume (Mac HD) to Sandbox, having booted from Mac HD. The "Important Note" warns that if one "did an initial copy using 'Backup - all files' ", then reverting to "Backup - user files" for Smart Update will delete all files on Sandbox other than the ones selected by the script "Backup - user files". I interpreted "initial copy" as the creation of Sandbox, which was apparently my mistake.
Whatever "initial copy" means, my question was, why would one use "Backup - all files" when copying/updating from Mac HD to Sandbox? Is there an advantage to that? The recommended procedure (p. 35-36) for both creating and (Smart) updating Sandbox is to use "Sandbox - user files and applications". I got a little confused by the apparently contrary scenario in the "Important Note" on p. 41.
I hope this makes the cause of my confusion clear. I'm still a little wary after my disastrous blunder on first using SD!. Dale Meyn.