I often need to flatten parts created by surfacing. An example would be an upholstry panel that has an irregular shape but the supplier then needs a flat pattern for cutting out the cardboard/foam. Typically I try to use:
FEATURE->CREATE->TWEAK->FLATTEN QUIT
If the geometry is quite complicating this may not work then I do use sheetmetal after converting it to a protrusion. Especially if I need to better control the rip. As for wether it's good modeling practice or not, I took a PTC approved sheetmetal course where this very topic was covered briefly. In some situation I see no other way of accomplishing the task.
Rob
