The default optimize profile, 'Screen', is suitable for most purposes. Files will look great on most screens, but may not be suitable for high quality printing or viewing on high definition screens.
'Print' can be used if high quality printouts are required. Files will be print-quality, but file sizes will be slightly larger.
'Mobile' can be used if files only need to be viewed on cell phones or PDAs. File sizes will be tiny, but picture quality may be poor on larger screens.
'Screen (no "flattening")' This has the same settings as the screen, however Embedded Objects in Office documents will not be flattened and will remain editable.
'Print (no "flattening")' This has the same settings as the print, however Embedded Objects in Office documents will not be flattened and will remain editable.
If none of the above options meet your requirements, you can create your own custom optimize profile.