Most of the research on fasting beyond 7 days shows that it's mostly going to only benefit weight loss. OMAD makes calorie management generally a lot easier. Most people have a hard time eating more than they should in under an hour or so a day. I mean, you could literally eat that much in candy, but most other sources would be difficult.
OMAD also allows for a longer, low-insulin and lower glucose window (depending on macro intake). The benefits will vary though. Eating 1-2 meals a day and not snacking or consuming anything sweetened (sugar or artificial) between meals is enough for most people to normalize their weight if not already obese and/or diabetic.
Eat clean first... cut the sugars, grains, legumes and refined seed oils (vegetable oils) first. Stop snacking second. 1-2 meals third. Longer fasting fourth. ... depends on how bad off you are. Some physical activity and weight lifting is generally beneficial but intake is the primary factor regarding overall weight and health.
In my experience, people tend to severely underestimate how much energy they are consuming, often neglecting to take into account chips (one of those small cans of Pringles has something like 400 calories) and more egregiously, sugared soft drinks which don't leave one feeling very full.