ref a. DoD Instruction 1400.25
To allow for DOD organizations to run smoothly you need to have some continuity in critical civilian positions. This has been easily done in the past by having the Commanding Officer of that organization decide whether or not to extend someone based on how critical their position is and if there are other qualified CONUS applicants that can fill the position.
With the implementation of ref (a), the CO will have to rely on higher authorities decision, even though they may have no idea what the impact will be at the local command level. Some positions are very hard to fill and replacing someone every 3-5years will be hard for both losing and gaining commands.
Additional factors to consider are the cost to train, adapt to foreign area, PCS cost, & morale.