Quote Originally Posted by flotulopex
Since I understood these command would be almost mandatory, it's beginning again to be a mess in my (small) brain.
"Almost" is the opperational word here. The DEFINEs are optional if you connect the LCD the way PBP assumes you will connect them: data lines DB4-DB7 to Port A.0 to A.3, RS to A.4, E to B.3.

If you connected your LCD this way then the defines are truly optional (and since you said your code did work without them then you had to have done just that).

The manual says just this, check page 95.