Many employers will simply lose touch with an old employee once they have left the workplace.
And while individual staff members may stay in touch via social media sites, especially LinkedIn, it is communication from the business itself that will often be left wanting. By sending out alumni newsletters, holding annual events that ex-employees are invited to or just dropping the occasional email you can go a long way in maintaining relationship that may prove valuable down the track.
Ex-employees with whom your business is still on active and amicable terms are valuable assets.
They make up a unique network who can recommend potential future employees to you or might be willing to come back to work for you in the future. Additionally, many of your old staff members will have expertise about your business that can not be found anywhere else, making them an amazing knowledge pool.
Treating old staff members with ongoing respect and attention will also improve the image of your company to current staff members, potentially improving your retention rates.