But what happens when your work is done -- who gets to come home to your spouse? Maybe your spouse will duplicate too, and then the lot of you can fight over the house. I won't go on; the social problems are obvious. Similar complications arise in the legal arena.
It may be worth considering a law prohibiting multiple active copies of the same person (where "same" is defined as anyone sharing any history). People would still be allowed to make backup copies of their brain information, to be activated in case of an accident. But to purposely duplicate yourself would be prohibited. An exception might be made for duplicates in separate star systems; assuming that no faster-than-light communication system is discovered, then the separation between the stars might be great enough to prevent serious problems.
This is a difficult issue which involves personal liberty and social stability. More discussion would be welcome.