As per my understanding, We can share the dashboards or reports by server and there is no need to have publisher license.
but If I have lots of file and lots of data and I want to ensure that different end user receive/access data/report according to their needs and status then I can do it via Publisher.
I may not be 100 % correct in my answer but yes Publisher functionality is related to more complex situations where we want to manipulate the access to reports to different end users.
hope this answer helps you
Anjana answer is correct and I would like to go into more detail. With server reloads all you are able to do is reload the document in place.
QlikView Publisher allows users to reload data in a QlikView analysis on a periodic basis to ensure that the most current data is available. QlikView Publisher also connects to directory servers within organizations and applies user security rules to a QlikView analysis to ensure appropriate user access. Finally, QlikView Publisher can alert end users to changes to a QlikView file and facilitate distribution via email or a web based interface called AccessPoint.