Many users of Asset Bank want to download an image in the highest resolution possible, for example for use in print.
The best way to enable this is to configure a Usage Type (for example called 'High Res (Original)') that has the checkbox 'Download Original' checked.
This will give the user the highest resolution image available for that asset. It may be tempting instead to set up Usage Type Formats for this Usage Type that (for example) convert the source file to a TIFF and change its colourspace to CMYK. This is pointless, for the following reasons:
The source file contains all the information available about the image - if this is a compressed JPEG then so be it. Although Asset Bank can apply interpolation, for example if you upsize an image, tools like Photoshop are likely to be better at it. Likewise with colourspace conversions.
TIFFs are generally much bigger than JPEGs, so all the you will achieve is slower download speeds for users.
In summary: give your users the source file if they want the highest res version available.