MSM is a form of sulfur that is a natural in many species biochemistry.  It is also a result of DMSO metabolism. It supports sulfur-based processes which include detoxification, inflammation, and secretion among others. Glutathione, one of the major detoxifiers of the liver, utilizes the sulfur in the cysteine component to attach to toxic molecules. The sulfur in cysteine can be supplied by amany of the sulfur sources listed here.  Cysteine as supplement is currently out of favor since it may be improperly utilized by certain imbalanced processes. 

As can be seen in the sulfur page (below), MSM is one of the least expensive sources of sulfur. Some authors feel that msm, taurine, nac, alpha-lipoic-acid and other forms of sulfur are interchangable to some extent.  Sulfur is needed for proper iodine metabolism. Finally, high doses of MSM are used by some people with rheumatoid arthritis and other forms of inflammation and arthritis with various degrees of success.

References

msm_amr_monograph_v8-4-438

MSM and DMSO – Organic Sulphur as a Versatile Healer

Effects of Methylsulfonylmethane (MSM) on exercise-induced oxidative stress, muscle damage, and pain following a half-marathon-a double-blind, randomized, placebo-controlled trial.2017.r

MSM promotes human periodontal ligament stem cells differentiation to osteoblast and bone regeneration

Dimethyl sulfoxide as an excitatory modulator and its possible role in cancer pain management – PubMed

MSM Files