Some owners manuals will suggest that a higher viscosity oil may be used under certain conditions. My 2021 Toyota RAV4 Prime (a plug in hybrid) manual "recommends" 0W-16 but then says "An oil with a higher viscosity may be better suited if the vehicle is operated at high speeds, or extreme load conditions." The manual does not further explain these conditions but the attendant Warranty and Maintenance Guide defines "Special Operating Conditions" as "Driving while towing, using a car top carrier, or heavy vehicle loading."
The owners manual for my 2012 Toyota FJ Cruiser (not a hybrid) says the same thing except the "recommended" oil is 0W-20.
The owners manual for my 2014 Honda Accord Plug In does NOT allow for the possibility of using a higher viscosity oil. It simply states to "use" 0W-20. Same thing for my ordinary Honda Accord Hybrid. So I've stayed with 0W-20 in these. I have 60,000 miles on the regular hybrid and it uses no detectable amount of oil between oil changes running around 6 to 7 thousand miles. Using a high quality brand of 100% synthetic, of course. 40,000 miles on the plug in Accord and again, no detectable oil loss between changes.
Passenger cars and SUVs achieve maximum weight capacity simply by filling them with passengers and luggage. I have seen high speed driving defined in these manuals as 70 MPH or more. So if you plan to ever fill your vehicle up with people, drive it on a high speed interstate, or like to accelerate hard, pull a trailer, mount a roof top carrier, the car manufacturer is strongly hinting you might not be best served with the "recommended" viscosity.
A 0W-20 oil is a 0 weight oil with viscosity improvers (VIs) that allow it to function as a 20W oil at operating temperature. These VIs are long chain molecules that are broken down as the mileage accumulates on the oil. So that means that 20W rating is gradually decreasing. By the time you need to change that 0W-20 oil it has become 0W-??. I'd rather not start this process with the 0W-16 that is only OK if you don't plan to push the vehicle very hard.
My plan is to go one weight higher where the owner's manuals allow it on the basis of extreme use. From 0W-16 to 0W-20 and from 0W-20 to 0W-30. Where there is no such allowance made by the manufacturer, I will stay with the recommendation.
My motivation is strictly what's best for my vehicle, not the environment.