The reasons I hear often for uneven stock splits are because one founder came up with the idea, or has been working on it for a month longer etc etc. When a company is in its absolute infancy, this seems like a logical conclusion but what about when the company is 5 years old? What we see is that even after only 3 months of YC when the founders are all working as hard as each other under stress and often the idea bears no resemblance to the original idea, that this starts to become a problem. The founder with less stock starts to feel like this is not such a good deal for him / her and it can lead to problems.

There are other reasons for uneven stock and as you mention, different levels of commitment or unequal status levels cause problems too. This is something that we would seek to understand more during the applications process when we see it and to try to make sure the founders have really thought through whether this is what they want. The key to a lot of this is open communication between the founders.

Of course, there are some situations where an uneven split does work. An example would be a founder has a mortgage and a family to support and therefore takes more salary in exchange for less stock.

We do not insist on an even split in any situation but I do always make sure that the founders think through their decision carefully.