If you are working on cars do you really need SAE sizes in you tool box anymore? I can't remember the last time I needed an SAE socket or wrench for my cars. How about you? Once again I'd like to free up space for items I use frequently.
I am with Donald. I find i use both on a daily basis.
I work on new car/engines/tractors. Along with ones dating over 100yrs old.
I never know what will come to my wrench next.
SAE and Whitworth wrenches are hanging on the wall the sockets are in another box, other than the occasional maintenance on the Ariens snowblower they don't get used enough to stay in the box especially the big sizes.
They are at hand if I need them just not littering my main box.
About 90% of the fasteners on the rear axle of a Nissan NP300 truck [work truck based on Frontier] are SAE up until 2015. From 2016 onward they are metric.
Drain and fill plugs, fittings on modern vehicles are often SAE.
English cars made in the 1970s had a mixture of the 3 systems. They switched from Whitworth to SAE in the late 1960s, then to metric about 2 years later.