In your blood stream all testosterone esters are converted to free tesosterone by catalaze enzymes. Therefore, the only difference between esters is how quickly they are absorbed into your blood (the half-life).
So, as stated above, the only reason to combine test esters is to get a cycle started quicker by using a low half-life ester like test prop with test enenthate (with is cheaper but has a longer half-life) for the first week or two of the cycle.
Or, to switch from a long half-life test to test prop or test suspension at the end of a cycle so that it leaves your body quicker and you can start PCT.