You can include almost anything in an Embedded Windows, or leave out all but certain core components.
A full install can install EVERYTHING, but the OS build could just be a text based console without a GUI, for example, the processing power behind a voice operated security clearance gate. Speak into a microphone, present a fingerprint, or enter a PIN and the gate lets you through, and logs you into the place, and out again when you exit, recording the data on a server somewhere.
An embedded system could present as a thin client on a low spec workstation running server-side applications, a set top box or a home theatre system, an information kiosk, not only a fixed device, but for instance a portable guide on a small tablet device in a museum capable of presenting further data about an exhibit, even packaging a cloud-based review of that particular museum visit for later study. POS systems linked to Warehouse JIT Stock controllers have already been mentioned.
Your automobile computer, GPS and in-car entertainment could also be running Windows Embedded, not only keeping the engine running efficiently, and in the right direction, but simultaneously providing music for the driver and a computer game or movie for the young passengers in the back.
Things like media center are just componentized parts of the Windows Embedded suite which uses the same codebase as the retail Windows 8, but you could just use Windows 8 RT components for a particular device.
Windows 7 Embedded Standard trial was certainly worth playing with, since you could build systems more-or-less indistinguishable from the Retail Windows 7 Ultimate OS with 90 days lifetime (or longer with education licenses), which could be extended if needed, but all the Windows 8 Embedded trials I have seen so far, timebomb your OS builds after 30 days, which doesn't seem worth the effort of building them.