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I would consider _your own tools_ as the central use case. Seriously, do you want to litter every `while read` (or your language's equivalent) with this pesky corner case handling?

```
while read -r line || [ -n "${line-}" ]
do
    : something with "$line"
done <"$input_file"
```

Having a single well-defined behavior also reduces the need for speculation. With malformed files, what exactly should `tail -n 1` return? Which line(s) should the `$` address in `sed` (which matches on the final line in well-formed files) match on?

You might argue what you think the "obvious" answer to these questions should be, but since that's non-standard behavior, you can never rely on these constructs to work portably, and so you are needlessly restricting the usefulness of your scripts.

As noted elsewhere, `cat` and `wc -l` on malformed files are another two use cases which commonly fail; but the vast bulk of broken tools will probably be local or informal tools which were never tested for this particular corner case.