Folders section is useful mainly for IMAP accounts because it allows to change the name of folders as the external Mail Clients perceive the Sent, Drafts and Trash folder. It allows users to integrate the Sent folder from WebMail with e.g. the Sent Items folder in Outlook Express.
By default, all folders are linked to the same names. If user needs to store sent messages in other folder because his/her Mail Client uses different name for such folder he/she has to change it in WebMail.
Small example in Outlook Express. After synchronization from Outlook Express when all the folders in WebMail are linked to the default names a new folder called Sent Items appears in the Folder List after logging to WebMail.
And the problem is that if user sends message from WebMail and checks 'Sent copy to sent folder' option the message is still stored to the 'Sent' folder and on the other hand if user sends message from Outlook it is saved to the 'Sent Items' folder. To integrate these two folders user has to change the Sent folder option in WebMail from 'sent' to 'Sent Items'. Then the 'Sent Items' folder disappears from WebMail and only 'Sent' is shown but if user synchronizes the 'Sent Items' folder from Outlook Express is synchronized with 'Sent' folder in WebMail.
The same can be done with Drafts and Trash folders.