Professional comments:
Olive oil is an oil, hence it is a type of fat. Fats are generally not considered healthy. There are different types of fats/oils, ranging from saturated (desi ghee) to unsaturated (mono and poly), and the best type is considered to be polyunsaturated omega-3 oils, these are found in certain types of fishes, they raise the HDL cholesterol levels and are therefore good for the heart. Monounsaturated oils reduce the LDL (bad) cholesterol, hence they also have good effects on the heart.
Monousaturated fat sources: Olive , Canola and Paenut Oils.
Polyunsaturated fat sources: Sunflower, Soyabean, Corn and Sesame Oil.
Should be use Olive Oil instead of other plant oils? (both are good for the heart, albiet by different ways): Answered by a PhD Nutritionist:
"It is better to reduce the consumption of regular plant oils (poly), rather than switch to Olive Oil and continue using it at regular/high levels".
Makes sense, as users of olive oil have the sense of reassurance that they are using healthy oil, and usually do not reduce the amount of oily foods they eat.
As a guideline, your monthly intake of oil should be 0.5 to 0.75 litres per month. Eg. in a family of 6, you should consume not more than 3 to 4.5 litres of oil per month.