A quick one today, it is entirely possible to install a copy of Windows Server 2012 without purchasing an activation key. This is extremely helpful in development environments where machines are very regularly recycled.
You achieve this by entering a Generic Volume License Key (GVLK), you can find the relevant key for your version of windows here:
Note that these keys are not the same as your paid-for or MSDN keys, they simply allow you to skip the enter key dialogue during set up.
So save those MSDN keys for servers such as your Domain Controller that are less likely to be thrown away and rebuilt.
In reality you would add these keys to the unattend.xml in your install media to avoid entering a key at all when building machines.
|Operating system edition||KMS Client Setup Key|
|Windows 8.1 Professional||GCRJD-8NW9H-F2CDX-CCM8D-9D6T9|
|Windows 8.1 Professional N||HMCNV-VVBFX-7HMBH-CTY9B-B4FXY|
|Windows 8.1 Enterprise||MHF9N-XY6XB-WVXMC-BTDCT-MKKG7|
|Windows 8.1 Enterprise N||TT4HM-HN7YT-62K67-RGRQJ-JFFXW|
|Windows Server 2012 R2 Server Standard||D2N9P-3P6X9-2R39C-7RTCD-MDVJX|
|Windows Server 2012 R2 Datacenter||W3GGN-FT8W3-Y4M27-J84CP-Q3VJ9|
|Windows Server 2012 R2 Essentials||KNC87-3J2TX-XB4WP-VCPJV-M4FWM|