[CronosPrime1]

That indicates that the numbers are floats.

I suppose the reason why it's needed is that the computer always needs to know what data type everything is. So in a normal variable declaration, you say something like

float distance;

This tells the computer or FRC controller that you are declaring a variable of type float, and the processor allocates a specific number of bytes to that variable. It's usually 4 bytes to a float. Since the memory allocation must be done before doing anything with the variable, variables must be declared before they are used, and they need to be declared as being a specific type because different types are allocated different amounts of memory.

In a macro, there is no keyword float. Thus, you need some sort of indicator showing of what type the constant or whatever is. Whoever made C decided that in a macro "f" would suffice for this purpose.

#define PI 3.14159265f