I think you'll get as many answers as there are opinions. FWIW, to me the line in the sand is drawn where you need to build it in a reasonably cost efficient m

I think you'll get as many answers as there are opinions. FWIW, to me the line in the sand is drawn where you need to build it in a reasonably cost efficient manner. (Which is to say, most science involves engineering to some degree. NASA and the LHC need to try to make what they do fit in some budget at the end of the day.)