what does the compression vest actually do?

[moobydo]

Is the purpose of the compression vest to minimize post-op swelling, and risks of complications associated with prolonged swelling, or is it to guide the inevitable internal scarring so that your eventual contour is more likely to be flat?  I'm just trying to understand what's actually at work when you have the compression garment on for 6 weeks or so. 

Also, for adjustable garments, is tighter always better?  I don't mean tight to the point of pain, but as tight as the garment can get (with those velcro straps) without extreme discomfort.

Thanks!