depends on your car and engine. Modern engines were designed with lightweight oil in mind and there’s no need to switch. Tolerances in manufacturing is much better these days versus 20 years back.When do you decide to change -w30 to -w40?
My car is now 76k mileage, I run penang KL once/twice a month, averages 2000 km a month
For example the 4G** and EJ** are very old engine designs.