It does spread but not aggressively. Sarcococca should be a mainstay for any shady PNW garden, IMO. I use it extensively in most of my designs......not always humilis but typically some form or another. One of the best shrub choices for dry shade.

It so far has been a very problem free shrub here but is prone to the boxwood blight that has started to rampage across the country so perhaps just a matter of time before it is less widely sold and planted.

Oregon Department of Agriculture - What is boxwood blight?

http://www.oregon.gov/ODA/shared/Documents/Publications/PlantHealth/BoxwoodBlight.pdf

It's great under low windows. I've never had any trouble with it.

I shovel pruned it because I simply could not smell it and without the scent it wasn't doing anything for me. It has continued to send up suckers even though the bulk of the plant has been gone two years. Still would not call it aggressive. It was just not right for where I had it.

I've never had any trouble with it

Box blight is new here, of course.