The 'Save Project As' shortcut allows you to save a new copy of the current project under a different name. New modifications will by default be saved in this newly created project, and your original project will be identical to the last time you saved it.
From 2.14 onwards, the name saved must be unique and a (1) or scaled up number as appropriate appended automatically. This will ensure that when interacting with other software (Enersight Link, Val Nav or Execute) the right project is always subsequently chosen as duplicates will no longer be able to be created.