For small home jobs, screw size is mostly about length, thickness, and whether the fastener matches the material, load, and pilot hole rather than about one universal best number.
A claw hammer and a rubber mallet solve different household problems, because one is for driving and pulling metal fasteners while the other is for controlled force without surface damage.
A good indoor step ladder should match ceiling height, storage reality, and stability needs rather than just offering one more rung than you are likely to use safely.