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.
Possible problems: timestamps other than 4/4.
Hell yeah!
A workaround would be to use a lower tempo and use the SDx command to delay a note to another tick.
(Its what I use)
You can't do the same stuff with low speed that you can with high speeds, though. If someone uses high speeds, he or she has a reason for that, I think.
Oh, I know!
Its just that s/he might want to know this in case s/he can't wait for the change to be implemented. :)
I/he/she can live without it, but a nice addition this thing would be :D