I don't use soylent, but use a similar product in the same space. I hope very few people are using these to replace _all_ of their diet. But as a tool, I find meal replacement mixes to be useful in multiple contexts:

- when traveling somewhere and I expect the options which meet my dietary requirements to be limited

- when trying to fit extra calories to gain weight

- when the other low-effort option would be snacks I won't feel good about (this used to mean the office)

Especially if you have a dietary restriction and a metabolism that requires a lot of calories to avoid unintended weight loss, arranging to always have nutritious _real_ food can require a lot of effort and planning, and I can't always be bothered. If the other options are eating too few calories, eating crappy snacks, or picking something at a geographically convenient restaurant, a meal replacement shake can quickly become best easy option.