This is just an additional option.
It seems to me that this is convenient in order to simply copy and paste to terminal, like:
npm add ... or npm remove ...

Example

> depcheck

Unused dependencies
* unused-1
* unused-2
Missing dependencies
* missing-1: ./index.js
* missing-2: ./index.js

> depcheck --oneline

Unused dependencies
unused1 unused2
Missing dependencies
missing1 missing2