It depends on how easily the "simple agreement" can be circumvented and how it would fail to provide money in case the business is unsuccessful. Even if a gree

It depends on how easily the "simple agreement" can be circumvented and how it would fail to provide money in case the business is unsuccessful. Even if a greedy optimist prefers equity to a salary, being paid later is worse than being paid sooner; not being a partner at the beginning is worse than having some authority; and being exposed to share-related shenanigans is worse than being owed a definite amount of money of certain value.