Analog signals are any signal that is characterized in terms of continuous time and continuous amplitude. The word "digital" is mostly used to describe signals that are both discrete in time, and discrete in amplitude. On some occasions, it is necessary to characterize signals that are discrete in amplitude OR time, but not both. Those occasions are less common.
A digital to analog converter is a device which takes at its input a digital signal and outputs an analog one. Conversely, an analog to digital converter is a device that takes in an analog signal and outputs a digital signal. These devices are incredibly useful in all types of audio electronics. This is because physical signals are always analog, such as a sound wave, the voltage on a wire, or the temperature of a room. However, many processing circuits can be implemented better or more cheaply with digital signal processing techniques than by doing all of the processing in the analog domain.
For example, when a music recording is made, many different channels are mixed down to a single (or stereo) track. While it is very common to perform this mixing with analog circuits, in many applications it may be desirable to perform some filtering, compression or other processing on all of the signals before summing them, and these functions are very accessible with DSP software. So, this would be accomplished by recording each track individually, and while recording, putting an ADC immediately following the microphone. Then, all of the channels are recorded in digital form, and they can be manipulated in the digital domain. If the final recording media is a compact disc, the final track must be recorded in digital form anyway, so there must be a conversion to digital at some point.
Another example is the playback of a CD. The songs on a CD are stored in digital form, so before they can be amplified and played through the speakers, they must be converted to analog through a DAC.
As for what makes this feature "special," well, I don't think it is special at all, considering that every receiver and component does it these days. Besides, they all get their DACs and ADCs from the same set of a few silicon suppliers.