A hint for an easier use:

Imagine you want to populate an area or volume with objects. In the dialog box you'd have to manually input the coordinates that delimit the area or volume, which can be a bit difficult. But there's an easy way. Simply do this:

Imagine you want to populate an area in the shape of a rectangle. Simply place an object (of those you want to replicate) in each corner of the rectangle (so, 4 objects). Select the 4 objects simultaneously and right click on the scatter/replicate tool. The coordinates of the 4 corners are already in the dialog box! No need to manually input anything, except the number of replicates you want (warning: if you input 10 replicates, you'll end up with 10 x 4 = 40 objects).

Of course, it's a similar method if you want to populate a volume instead of an area. You just need to have 8 objects instead of 4. :-)