On the Migrate page tab there are 2 sub pages: "Migrate Help" and "Update .mshc".
The Migrate page takes a copy of your help project then converts it to HelpViewer format. Then it zips the output to a .mshc help file. See Migrate
The Update page tab is similar to the last part of the Migrate command. It checks/fixes syntax (optional) and zips the specified folder's content to a .mshc help file. The dropdown allows you to also validate or fix the XHTML syntax before zipping. Usually the migrate command works on a copy of the original help in the _HelpSource folder. If you point the update folder to your projects _HelpSource folder then you can work on that folder using Update page tab to recheck and rezip.