What is the effect of a semolina/plain flour mix in pasta making? I have made fresh egg pasta a couple times now using various combinations of semolina and plain flour (4:1 semolina to plain flour, 4:1 plain flour to semolina, all plain flour).

Seeing as semolina flour is more expensive than plain flour, what's the effect of the semolina/plain flour mix on the texture and flavour meant to be? Perhaps the distinction is lost on me, but for me all the variations taste roughly the same.
Firstly, all-purpose, high protein ("OO"), semolina, whole wheat and other flours make excellent pastas on their own or in combination.  So, at the end of the day, you should use what you like, have on hand or is economically feasible.  Semolina flour, either by itself, of in combination with other flours, should not impact the flavor much...but it should create a slightly "rougher" texture.  Some claim that this helps sauce cling better, but I have never done a side-by-side comparison.