It’s just a question of calories. Each tbsp is 120 calories. Over a month, for example, an extra 120 calories per day adds up almost exactly to an extra pound of bodyfat (assuming no change in energy expenditure, which probably is not an exactly correct assumption but which serves for illustration anyway.)
So if keeping calories pretty tight, the added tbsp either has this effect or one has to for example reduce protein by 30 grams per day, or carbs by 30 grams per day, or some hybrid of those two. It might be chosen to use only 2 tbsp per day for those reasons (I do when on quite low calories.)
HK and pvieira are certainly right that inherently there’s nothing excessive at all about 3 tbsp/day and it can be perfectly appropriate or actually preferred.
On the research, I haven’t seen anything that tried to determine a dose/response curve. But a fairly typical value in studies showing body composition benefits to olive oil intake had diets with 20% of calories from MUFA.
So for example on a 2000 cal/day diet that would be 400 MUFA cal/day, which would be 44 g MUFA per day.
Since each tbsp of olive oil has 10 g of MUFA, three tbsp is hardly excessive if the calories are no problem.
But if the calories are a problem, two tbsp seems to be substantially helpful even though below that studied value.