Merging a user is not a common practice by most managers. Some practical applications of when to use this would be when a salesperson gets married and has a new name coming in from traffic, if a salesperson leaves and you want to reassign their entire book of business to another salesperson, or during a traffic system conversion in order to clean up names that may filter in after a conversion.
When you want to merge a salesperson into another salesperson, navigate to the User List, Click Users (Located on the left in the Navigation Panel). Hover over the Account Executive that you wish to merge and click on the Gear Icon then select Merging Options.
Search Box - Simply type in the name of the salesperson that you wish to merge the current user into.
Items merged to - Displays a listing of previously merged salespeople into the one that you are currently viewing.