Everyone needs methylation. We'd be dead without it.
The mistake most people make is in not testing to see what's going on and then supplementing to normalize it.
Its more than folate and MB12. You also night need B2, B6, trimethylglycine, magnesium, amino acids (cysteine, glutam8ne, glycine, and maybe methionine), molybdenum and B1. If you don't have all of those in place in the right ratios, you will very quickly run into trouble with a variety of symptoms - depression, anxiety, headache, intestinal discomfort, sulfur gas, farigue6, etc.
Even if you have everything in place, you could be mobilizing toxins you've been carrying around. If your digestive system isn't eliminating things well, you're not ingesting enough fiber, water, B1 and molybdenum) the toxins can get reabsorbed, making you feel sick. Many people take binders to bind the toxins. Having good gall bladder and liver function helps too.
As you can see, there's a lot to it, and many places to make mistakes in putting together a protocol, especially if you're pulling someone else's canned protocol from the Internet or taking some canned methylation supplement.
And, your needs may dramatically change over time. Mine have, yours will too.
The best test is the Genova Diagnostics NutrEval FMV with Amino Acids. It measures the values of all the nutrients involved.