What's the point of choosing the reference direction of current to go from low to high potential? In my textbook the author sometimes chooses the reference direction of the current $I$ to go from low to hight potential, from $-$ to $+$ and sometimes from high to low potential $+$ to $-$. I have understood this reference direction does not really matter for calculations except for the sign of some results.
But I just can't understand why one would ever intentionally choose $I$ to go from low to high potential when the accepted convention is that current always go from high to low potential, why would you intentionally choose the reference direction to contradict the convention of how current flows?
I have read this question and this question that also asks about reference direction for current but I think the answers more explain why the choice of reference direction is not important for the end result, not why one would choose the reference direction to contradict the convention in the first place.
 A: 
. . . . when the accepted convention is that current always go from high to low potential . . . .

The conventional current (flow of positive charges) does not always flow from a region of high potential to a region of low potential.   
Have you considered the example of a battery which is being recharged where the current flows from the positive (higher potential) node through the battery to the negative (lower potential) node?
The are other examples of circuit elements where the current flows into the node at the higher potential eg a capacitor being charged and an inductor with an increasing current passing through it.  
For a resistor you can away be sure that the current enters the node at the higher potential but for other circuit elements this is not necessarily true.
These examples show that the direction of current can't be defined in terms of the potential. The way the sign of current is actually defined is as follows. The current flows from region A to region B if A's charge is decreasing and B's is increasing. In other words, it's defined in exactly the same way that we define current for a physical substance like water.
