1st thing to know is if you check one or both options then that's what it does instead of rebuilding. There should be radio buttons instead of checkboxes to make that clear. Integrity check checks for only a small subset of types of corruption so it's usage is pretty limited as in worth skipping. Optimize came from a request from the Support Dept. It creates a new empty file then copies all the data from the original file. It's a good option. It does what @DavidOverholt said.