Lead History section will give you an outlined detailed view of the representatives who have interacted with the lead or viewed it, previous dispositions added, time and date stamps. This area is a great road map to understand the behavior of a particular lead.
On any lead you can view the lead history by selecting the Lead History tab above the lead information.
You can access the lead history while feeding through a campaign or by searching for a particular lead using the search icon in the top right corner.
The following is an example of a Lead History. 
Based on the above lead history I can see which representatives have interacted with it in the past and when.
In this case I can see that the lead was fed most recently from the campaign, most importantly I can see the last disposition added to the lead, which was 'Callback'.
From this screen shot I can see all the previous dispositions, all the representatives and the time and date that the lead has been handled.
Giving a complete understanding of the Lead's History.