Could you please explain why whole genome sequencing at 0.4x coverage is worthless? I would have thought it could provide a lot of value, for example, to understand inherited health risks and to predict drug response.
But the parent is a bit wrong, it's not worthless. The reason people sequence at <1x is because you can still statistically derive a lot of useful info especially about larger variation - long segments of the genome that are deleted or duplicated etc can be inferred, and there is a technique called "imputation" which means if you measure one part of the genome well you can usually predict the nearby parts with surprising accuracy.