I was reading Harlan Brumm's blog and came across a great tip that is often overlooked. How do I know it's overlooked? Well, I have to say I never even noticed it myself! Or maybe I did but cannot remember, who knows?
You can read his post here. Also, see the attached image for further reference. I'm going to paste his post below too.
------------------------------------------------------------------------------------------------------------------------------
When you select an array in Revit the Options bar displays a check box for ”Append to End”. What does this do?
Append to End allows you to change how elements are added or removed from an array. When you first create an array in Revit, the option bar gives you an option to choose to move to: 2nd or last.
This determines whether or not Revit will attempt to place the number of items in the array between the two positions you chose while making the array (Last) or if Revit will keep adding elements to the array on the end based on the distance between the two elements that you place during its creation (2nd).
Append to End allows you to switch this behavior after you have created the array. If the Append to End check box is checked, this means that elements added to the array will be added to the end of the array based on the current distance between the elements. If the check box is unchecked, Revit will space all the elements in the array equally between the first and last object.
A little hint:
In order to see the Append to End check box you need to first select a element in a Array, and then selected the line that displays that defines the array. Selecting the number that appears above the line will allow you to change the number of items, but selecting the line itself will allow you to change the Append To End setting on the options bar.