What the smoke point actually measures
The smoke point is the temperature at which an oil begins to break down visibly and release smoke, signalling the formation of off-flavours and undesirable compounds. Refined oils such as avocado and refined olive oil tend to have high smoke points (often well above 200 degrees Celsius) because refining removes free fatty acids and impurities that lower it. Butter is intermediate, partly because its milk solids brown and burn. Unrefined flaxseed oil is low and is poorly suited to high heat.
Higher smoke point generally means an oil tolerates higher-temperature cooking, such as searing or stir-frying, before degrading.
Smoke point is not the whole story
Smoke point is a useful guide but not a complete measure of an oil's stability or healthfulness. Oxidative stability also depends on the balance of saturated, monounsaturated, and polyunsaturated fats, since polyunsaturated oils oxidise more readily even below their smoke point. Antioxidant content, as in extra-virgin olive oil, adds further protection. Published smoke points also vary by refinement and freshness.
This is general educational information about cooking chemistry, not dietary or medical advice. Choices about cooking fats and heart health should be discussed with a qualified professional.