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Maybe this image helps a bit, offset rim helps to make the hub-rim-spoke triangle more even and allows for more even tension between the drive and the non-drive side of the wheel, which makes a stronger wheel. As @Emyr pointed out a longer freehub body results into a less even tension than a 'normal' shorter freehub body. An offset rim helps to compensate
tldr left triangle is more 'even' and therefore stronger
Well yes and why seems it more relevant with 11 speed? Only ever had 10 speed not offset. Explain please.