When viewing a report, it is possible to change the scope of the time frame of the report without having to manually add new columns. This means if you're viewing a report for the current month and wish to see it for the whole year to date, you can accomplish this without needing to use the column selector to pick the year to date versions of the month columns already in the report.
In the lower right corner of the report is a tool labeled Time Periods. In a blue text clickable link will be the current time frame being displayed on the report.
Clicking the blue text link will present a menu of all the other available for the report. Select from the available time frames. This will cause all of the columns on the report to change from the currently displayed time frame to the newly selected time frame.