I want to make clear that this question is not a criticism of either way of doing it, as I think both work. But in turn based or mail play, when both sides of an opening are played, do you favor completing one game before the next one is started of playing both games concurrently?
Snail mail tournaments have the players play the two sides concurrently (this is also the practice in correspondence chess where each pair of opponents play two games). That was necessary because snail mail takes a long time. Wyllie and IYT have followed suit. Over-the-board tournaments obviously play them sequentially, and Gold Token does it that way.
I can see advantages to each. If two players wanted to play quickly, it makes sense for them to concentrate on one game before going to the other, and there is not the temptation of waiting to see what your opponent does as red before you decide what to do as white. On the other side, if you play many opponents, and can handle a move in each game each night, you will finish sooner, and any advantage or disadvantage at getting the weak side first will disappear.