It works in most trivial cases, so I'm assuming it's widely done irl.
Imagine building some small app that reads external config file. You personally only care about yaml files, but your avid users ask for official json support as well because of a few of their files.
It's not high priority, but as you remember the old saying, json is just a subset, so you try a bunch of files, confirm it works well enough, and decide to pipe JSON files to your yaml parser as well. Done and done.
And it's not so big block of code or anything that jumps at the users, the dev just happens to share a parser between formats.
Imagine building some small app that reads external config file. You personally only care about yaml files, but your avid users ask for official json support as well because of a few of their files.
It's not high priority, but as you remember the old saying, json is just a subset, so you try a bunch of files, confirm it works well enough, and decide to pipe JSON files to your yaml parser as well. Done and done.
And it's not so big block of code or anything that jumps at the users, the dev just happens to share a parser between formats.