There has been fierce debates over balance shafts - to delete or not to delete. From factory the rods and piston assemblies are within a few grams of each other so getting a die grinder out and shaving a little metal off the heaviest assemblies will bring everything to near perfect without machining and balancing the crank/flywheel assembly. There are plenty of engines that don't have balance shafts in them and were in production up to early 2000's - they don't try to knock themselves apart or massage your legs under throttle...

Pros - rotating mass reduction. Improves throttle response, adds horsepower. Eliminates balance shaft bearing failure and deletes the secondary timing chain (balance shaft bearing failure leads to catastrophic oil pressure loss and RIP to bottom end) Subsequent improvement to primary oil pressure.

Cons - some people have experienced secondary harmonic vibration in certain rev ranges, to the point where they felt it was unlivable.