Rehiring a former employee can be good for some reasons:
Firstly, having known about your business, company and workplace; provides former employees an advantage over possible recruits who needs weeks or even months to learn the ropes.
Secondly, rehires return to your company after having experienced outside and probably, developed new skills.
Finally, every returner gives a clear message to other employees that the grass is not always greener on the other side of the hence.
As rehiring is a valuable asset for the company, here are some list to increase the number of your “boomerangs”:
Find out and cure the problems that caused the employee to leave your company. Best way to do is exit interviews and direct investigation.
Keep in touch with your valuable departed employees. You should use alumni programs or alumni relation tactics. Try to communicate with them occasionally, keep them updated about your company and ask how they are doing in their new jobs.
Pave the way for re-employment. There is a discomfort and some doubts in returning to old company, remove these with public statements and make it easier for the former employee.
Probably the most successful comeback in business world was rehiring of Steve Jobs who returned to his former company as wiser, more experienced and skilled. Your rehire may not make the same impact but it is likely to be more successful than a person you know nothing about.