What is the use of Subscribe and Unsubscribe commands in Imap4req1?

Question

What is the use of Subscribe and Unsubscribe commands in Imap4req1? I checked RFC 3501, but i could not understand its use. What will happen when i write following commands

A SUBSCRIBE "MAILBOX_NAME"

A UNSUBSCRIBE "MAILBOX_NAME"

will server treat those mailboxes as separate one?

Sample :

please check below once, and tell the difference

A LIST "" "*"
* LIST (\HasNoChildren) "/" "Bulk Mail"
* LIST (\HasNoChildren) "/" "Draft"
* LIST (\HasNoChildren) "/" "Inbox"
* LIST (\HasNoChildren) "/" "Sent"
* LIST (\HasNoChildren) "/" "Trash"
A OK LIST completed
A SUBSCRIBE INBOX
A OK SUBSCRIBE completed
A LSUB "" "*"
* LSUB (\HasNoChildren) "/" "Bulk Mail"
* LSUB (\HasNoChildren) "/" "Draft"
* LSUB (\HasNoChildren) "/" "Inbox"
* LSUB (\HasNoChildren) "/" "Sent"
* LSUB (\HasNoChildren) "/" "Trash"
A OK LSUB completed

Averment

Answer 1

They change the output of the LSUB command. That's it. SUBSCRIBE adds folders to the output of the LSUB command. UNSUBSCRIBE will remove them from the output of the LSUB command. That is, LSUB shows only subscribed folders.

LIST will always show all folders.

For example starting with all folders subscribed:

a LIST "" *
* LIST (\HasNoChildren) "." "INBOX.Drafts"
* LIST (\HasNoChildren) "." "INBOX.Sent"
* LIST (\HasNoChildren) "." "INBOX.Trash"
* LIST (\Marked \HasChildren) "." "INBOX"
a OK LIST completed

a LSUB "" *
* LSUB (\Marked \HasChildren) "." "INBOX"
* LSUB (\HasNoChildren) "." "INBOX.Drafts"
* LSUB (\HasNoChildren) "." "INBOX.Sent"
* LSUB (\HasNoChildren) "." "INBOX.Trash"
a OK LSUB completed

Now let's unsubscribe INBOX.Sent:

a UNSUBSCRIBE INBOX.Sent
a OK Folder unsubscribed.
a LSUB "" *
* LSUB (\Marked \HasChildren) "." "INBOX"
* LSUB (\HasNoChildren) "." "INBOX.Drafts"
* LSUB (\HasNoChildren) "." "INBOX.Trash"
a OK LSUB completed

All that's different is that INBOX.Sent has been removed from the LSUB output. Note that LIST output will not have been affected at all.

Now let's put it back:

a SUBSCRIBE INBOX.Sent
a OK Folder subscribed.
a LSUB "" *
* LSUB (\HasNoChildren) "." "INBOX.Sent"
* LSUB (\Marked \HasChildren) "." "INBOX"
* LSUB (\HasNoChildren) "." "INBOX.Drafts"
* LSUB (\HasNoChildren) "." "INBOX.Trash"
a OK LSUB completed

They are generally used for a client to mark folders the user is interested in seeing.

Patti