The less an interpreter piggybacks, the less will be left over to implement when porting the interpreter to another platform. That benefit's enough by itself, IMO. ^_^
But then I tend to care more about the work I'll need to do in the future than the work I do today. When my priorities are the other way around, like for fun-size DSLs that'll hopefully never need porting, being able to piggyback is nice.
