A resignation is an opportunity to discover information concerning why that employee is leaving you.
The steps to take are:-
1) Get the resignation in writing
2) Hold a meeting to discuss reasons for leaving
3) Acknowledge the resignation and/or take appropriate action
You can find out if there are risks to your business such as your employee going to work for a competitor or if they are leaving because they think they have been mistreated.
Miss these steps and you might miss the early signs of a potential legal claim in the future.