There are some fundamental chemical processes that go on in the body. Acetylation, sulfation, arylation, methylation (a kind of alkylation), etc. Methylation in particular is important at least because it is involved in how our DNA is used.
Another thing that methylation does is it deactivates histamine. (Histamine is also deactivated by oxidation.) If you don't methylate well, you end up with a lot of histamine, is how I understand it. Just as one consequence. Lots of histamine can be an issue. It affects inflammation, immune response, and neuronal behavior.