LNT is useful because you work with an abundance of caution when it comes to radiation. It's difficult to know what type of radiation someone received and where. Both of these can dramatically change the risk of exposure. It's not hard to measure in a lab, but an accident isn't a lab and you can't just go placing sensors all over every radiation worker's body (at least yet. Small sensors embedded in clothing would change this).

So what do you do? You purposefully over estimate. Because if your estimate is wrong, the human is much more likely to survive if you incorrectly assumed they received more than they actually did than if you error by assuming they got less than they actually did. Failure analysis is a critical part to any engineering or safety plan.

Why not over estimate as much when higher dosages are received? Well that's because it matters a lot less. As dosage increases all those nuances of where and what type matter less (they still matter).

It's still all highly complex and what I'll say is that if you haven't spent at least a year studying this stuff you're more under water than you think. It's great that there's a lot of educational material out there but unfortunately when it comes to complex topics like nuclear many of them do more harm than good. Pro nuclear armchair experts tend to be as uninformed as anti nuclear armchair experts. So like the LNT, it is always good to work with an abundance of caution. Especially when talking about complex subjects on the internet