An S shape has the advantage of resonance reduction. The two bends add rigidity to vibration compared to a straight tube and flexural waves will be attenuated. Also a larger tube is more rigid than a small tube even if they weigh the same (tubes have good rigidity for their mass compared to a solid rod). Light weight straight tone arms have the increased risk of unwanted resonance due to standing resonance waves along the entire length.
Only advantage of straight is they are cheaper to build and can have lower mass for high compliance cartridges.
Only advantage of straight is they are cheaper to build and can have lower mass for high compliance cartridges.