What is Device Link Profile?

In a normal workflow situation, the color space of the input device is transformed to the color space of the output device via the device-independent L*a*b* color space (known as the profile connection space). This process requires two different profiles — a source profile and a destination profile. 

Color conversion using source and destination profiles

A device link profile is a special kind of ICC profile that converts the color space of the input device directly into the color space of the output device, whereby the output device can be either a physical printer or a file format. Unlike ordinary source or destination profiles, they do not describe a specific color space, but define the conversion from a source color space to a destination color space. The basis for creating a device link profile is, therefore, always an ordinary ICC profile. 

Device link profiles are most commonly applied to direct CMYK-to-CMYK transformations because converting via a device-independent color space can lead to undesirable effects, such as unsmooth color gradients. In a device link profile the color separations are maintained, thus preserving the black channel of the source profile. 

Color conversion using a device link profile

Indeed, preserving the black channel of the input color space is one of the main advantages of using a device link profile. For this reason, device link profiles are often used during data preparation, e.g. to convert from ISOcoated to ISOuncoated. 

Furthermore, device link profiles enable you to by-pass the L*a*b* color space, thus preventing contamination by other colors, e.g. 50% black stays 50% black. 

However, you should be aware that device link profiles are not as flexible in use as other ICC profiles. Each device link profile can only be used for the specific combination of source and destination profiles for which it was created. 

source: http://www.efi.com/