The copper coil I would assume is replacing a steel tube of much shorter length. I believe the reason is two-fold -- on mine, those steel tubes get hella hot, way way way hotter than the 50-60C the head temp probe shows. So the copper coil should radiate more heat away from the system. Being cooler, it may increase condensation out of the compressed air as well. Is copper rated for these kind of pressures? Hope the guy knows what he's doing...This setup looks much less complicated than mine. On my Vevor YH clone, there are 3 steel tubes running back and forth, between stages and manifold blocks. The manifold blocks both have valves/drain screws that release pressure and let condensation out. I can't tell where on this video the condensation drains out of this compressor.I just noticed the copper coil does a U-turn after one of the connections -- if this is a safe modification, it still needs refining.
With that setup you would benefit most from a good dual final filter, than messing with the tube coil, it may increase the piston seal life as the incoming air would be a bit cooler though