Visually it's similar to the "Grow/Shrink selection" commands, except it applies to the whole pattern and that you don't actually modify anything, but rather omit the display of rows.

For example, an x1 zoom renders everything, x2 shows one in two rows while x4 only displays 1/4 and so on.

This is useful when working with high speed tunes where you can lay down the basic structure at high zoom(like x4 or x8), which lets you see the big picture and then going with x1(no zoom) when working on details like manual arpeggios.

As a small extension to this idea, maybe have a small, 1pat wide window with 1x zoom, while the normal pattern display is at 4x/8x.