All backup operations (such as copying, purging, and so on) occur when you save changes to a project. If necessary, you can use backup files to roll back the latest changes to a project, restoring the project to a previously saved state.
When you save a project, Vasari makes a backup copy of the previous version of the project (that is, the project file before the current save). This backup copy has the name <project_name>.<nnnn>.rvt, where <nnnn> is a 4-digit number indicating how many times the file has been saved. The backup file resides in the same folder as the project file.
You can specify the maximum number of backup files that Vasari saves. (See Specifying the Number of Backup Files.) If the number of backup files exceeds the maximum, then Vasari purges the oldest files. For example, if the maximum is 3 backup files, and the project folder contains 5 backup files, then Vasari deletes the oldest 2 backup files.