Familiarize yourself with the things to consider before you merge duplicate lead records.
Salesforce associates any related items from the duplicate leads, such as campaign or activity information, with the newly merged lead.
If you’re merging duplicate leads that are members of different campaigns, Salesforce retains the campaign Member Status Updated
The newly merged lead displays the Created By Modified By fields
The master lead replaces the duplicate leads in all the requested meetings they were invited to. Also, all meeting messages written by the duplicate leads are automatically associated with the master lead. (Meeting messages appear on the requested meeting's Web page and are visible to all invitees.)
The master lead replaces the duplicate leads in all the scheduled meetings that the leads were invited to. But make sure to add the new master lead to the meeting invitee list in the scheduled meeting.