There are alot of things that can result in someone not giving the company their best work and undivided attention during work hours. A wedding, a divorce, birth of a child, illness of a family member, personal illness, impending Super Bowls, etc. HR people are generally tuned into paying attention to these things, and in fact we have laws on the books to help deal with these to an extent. Well here is one more thing that can cause a major distraction: a personal relocation! When it is a corporate relocation there is some support for the move and typically some financial backing and assurances. But when it is a personal relocation there is a great deal of stress associated with timing, money, and time issues. Making sure the appropriate things are canceled and the other approriate things are turned on. Packing, movers, and finding temporary housing all compound the stress.
The stress increases when the sale of a home is involved because then real estate dealings are involved, potential buyers viewing the house, and once a buyer has committed you have the stress of making it through a closing, Money, timing, repairs (and more money), delays, the movers, etc. all cause your employee to be distracted and subsequently less than productive at work. ( I know this from personal experience because I just described me!).
So be aware of what is happening in your employees personal lives because you may be able to anticipate stressful times that may have an effect on their work. Your awareness and proper handling of these situations may make the situation smoother for all parties concerned.