Aesthetics matter
The example that he gives is this:
From all the card's properties which one generated most complains? The lack of symmetry. The number seven is missing from the mana cost. They probably went with a mana cost of eight, four colorless and four black mana, for power level reasons. Could they had made it 7 + 1 or 7 + 2? I don't know how they decided on the cost. Nonetheless, having a number seven on the mana cost would probably have felt better.
There is a lot of research about symmetry, asymmetry and perception. There are even some disorders or cognitive deficits related to that but I'm not going to discuss that. Let's see some practical examples. The brain naturally searches for patterns and this does not depend on language or culture. It's universal. See this building's facade with symmetrical windows:
Credits: bernswaelz (pixabay)
All windows are the same. Same shape, same curtains, same light inside. Had one window been different from the others the lack of symmetry would've drawn the attention to the window that stood out. If the asymmetry is intentional, good. However, if it wasn't intentional we have a problem. Sometimes the lack of symmetry confuses the player because it draws the player's attention in some unwanted direction. The same could happen inside the building with a door that isn't equal to all other doors.
Credits: AlphaYellow
See the ship's engine's room in Max Payne 3. The engines and lights are all symmetrical. It's more pleasant to the eyes and this is more about aesthetics than being realistic or functional. It'd feel bad had it not been made symmetrical. Right after that room the player goes through a corridor that is also symmetrical with showers on both ends to the left and to the right. For the same aesthetic reasons there are symmetrical showers on both ends. The corridor itself has symmetry but the objects themselves don't. The symmetry of the space itself is more important than having the objects symmetrically placed in this case.