What problem does this feature solve?

At the case of presenting position distribution of cars, with the functional option symbolRotate, we can make the car symbol rotate by driving direction(a numeric angle) of each car, but not always be the same.
For example, if driving direction of a car is south-east, the symbol of it will perform a rotation through 45deg.

What does the proposed API look like?

symbolRotate of scatter series can be a number(now provided) or a function(requested)