to limit the amount of data being loaded in to the watchlist to reduce your system's resources. By default we load one year of data for each symbol for the column calculations. If you have custom columns with your own formulas that require more than one year of data to be calculated (eg 2 year % change) then this value needs to be increased.
to calculate the columns as of a specific date. By default the watchlist will use the most recent data available, but if you wanted to see the data as of the end of the previous month you can set it to Date Range and select the Date to Load To.