Date#() lets you explain to QlikView how you want a date value to be evaluated.
If I have a date in the following format 2012 04 10 to represent 2012-04-10 it might not be understood automatically as a date by QlikView.
In this instance I can use date#() to show QV how to interpret the value:
date#('2012 04 10', 'YYYY MM DD')
This will attach the proper underlying number to the date value for calculation purposes. (The date number is a counter starting with 1899-12-31 = 1 and then increases with 1 for every full day since.
If you want to reformat the date into another format you can slap a Date() function around the Date#() function. The Date() is there to define the format you want to show the values in, while the Date#() is to define how you want to interpret a value as a date.
