640,000 total points ~ 64mB file size
While sculpting in ZBrush your files can be as large as your system can handle. I usually sculpt at or around 4,000,000 points. To output your file for 3D printing however, you must decimate the model to 640,000 total points, or fewer, before you export to .stl format.
All 3D printers will print faster with smaller file sizes and most service providers (shapeways.com, matter.io, i.materialize.com, etc...) require that you keep your files below 64mB.
--- just some notes for me to reference in the future.