Do not understand the --from-json feature

### Description

> Hi there, I am confused about the --from-json freature
>
> Is it a feature to convert one output to another litke from json to json-pp,
> or is it a feature to import the last scan result, so that the scantime itsef could be improved, because it is scipping anything it
> already had have scanned in the last scan ?

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- [ ] Inconsistency
- [ ] New Section Request
- [ ] General Improvement
- [ ] Typo/Mistakes
- [x] Other