It depends what you want A3 for. For example, in my case I often need hard copies of an airliner's "LOPA" (Layout Of Passenger Acommodation). Just as already said, the original drawings are pretty detailed (showing position of every portable fire extinguisher, defibrilator, first aid kit, portable oxygen set, etc, as well as seats, cupboards, loos and galleys, etc, etc). Being so detailed the originals are normally produced in A0 or A1 and I normally receive them in .pdf files. Printed out onto A4 there's just too much detail to be useful/clearly visible, but A3 works fine.
That's just one example, and I guess it's much the same with architect's plans, builder's drawings, etc.
BTW, my cp 1700 was not all that expensive (compared to a normal A4 colour ink jet printer) but as said, that was a long time ago - at least 10 years ago I guess.
AES