Inbox Repair Tool

I was recently asked to recover a personal folder (*.pst) in MS Outlook that was almost 1GB in size. The user had setup delivery of Email directly into her personal folders and her Hard drive filled up while she wasn’t looking. The .pst file was damaged and I attempted to run the Inbox Repair tool after moving the file to a network folder. The repair tool reported over 1100 errors and failed to repair the file. What are the limitations of this tool and how does it work?