What are pros & cons of drain tubes after lipo? What determines if drain tubes are used?

I'm not really sure where you would place a drainage tube after liposuction. They are not part of the procedure. If liposuction is combined with an operation that creates a dead space such as an abdominoplasty some surgeons may choose to use them in this situation.

In my experience, post operative drains are not commonly used in liposuction. Usually compression is adequate to mitigate the risk of fluid collections and achieve a smooth post op contour.The exception is large volume liposuction and the use of laser liposuction. Larger volume aspirations using SmartLipo/Laser lipo tend to be more prone to collections. For patients with aspiration volumes greater than 1500cc (using laser), I will typically leave a single drain behind. However, protocols will vary from one practitioner to another.As always, discuss your concerns with plastic surgeon certified by the American Board of Plastic Surgeons. 

Thank you for sharing your excellent question.  If only liposuction is being performed drains are not routinely placed. If however liposuction and say a tummy tuck is done then I typically use drains.  Your surgeon will be able to offer you the best advice based on your specific procedure.