The compact command cleans up fragmentation but also eliminates any padding factor, which can have a big performance impact if you're doing a lot of writes that grow documents. It would be nice to have an option to compact to make it remove fragmentation while retaining padding. One approach would be to leave the same padding as was there previously (may not be possible if there's no way to distinguish padding from fragmentation), another would be to add the current padding factor to every document, and another would be to let the user specify what padding factor should be added to the documents.