Q:

Precession in the vector model of angular momentum - quantum mechanics?

The vector model of angular momentum in quantum mechanics says that, for example, the angular momentum vector $\mathbf{L}$ precesses about its projection on the $z$ axis, like this:

We can add $\mathbf{L}$ and $\mathbf{S}$ to make $\mathbf{J}$, so that $\mathbf{L}$ and $\mathbf{S}$ precess about $\mathbf{J}$, like this:

NOW:
1) Does the direction of precession (clockwise or anticlockwise) matter?
2) This is just a model, $\mathbf{L}$ and $\mathbf{S}$ do not actually precess, right?
So why do use this model?
Is it a way to take into account the fact that we don't know $L_x$ and $L_y$?

A:

My quantum mechanics teacher, always say to me, that those models for "see" the spin and the angular momentum, are not correct. 
the reason is that the picture of an electron precessing associated with the spin in't correct because  the spin is'nt associated with any spacial coordinate. in quantum mechanics is better abandon those pictures, the important are the properties of L and S and the measure. 

