What YAML is
YAML uses indentation instead of brackets. It is a superset of JSON, supports comments, and is meant to be edited by hand.
Kubernetes manifests, CI pipelines, Ansible playbooks and most modern config files.
What Plain Text is
Plain text here means columns lined up with spaces, the way a command line tool prints a table.
Terminal output, log files, fixed-width exports from older systems.
What changes when you convert YAML to Plain Text
A YAML list of maps reads as rows and columns directly. Anchors and aliases are resolved before the table is built, so a repeated block arrives expanded rather than as a reference.
Columns are padded to the widest value. Width is counted in display columns rather than characters, so a table containing Chinese, Japanese or Korean text still lines up: those glyphs occupy two columns in a monospace font.
What carries over from YAML to Plain Text
YAML records 4 things about a table that plain text has no way to hold.
YAML distinguishes a number from the text of a number; plain text does not, so every value arrives as text and has to be re-parsed by whatever reads it next.
An empty cell and a missing one are the same thing in plain text, so a null and an empty string in the YAML both come out blank and can no longer be told apart.
YAML can hold a value that is itself a list or an object. plain text has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
A line break inside a cell ends the row in plain text, so line breaks are replaced rather than carried through.
The keys stop being repeated: plain text writes the column names once at the top, so the same table takes noticeably less space.
The identifier 007 comes out of the Plain Text as 007. Reading it as a number would have made it 7, and an id that changes value is worse than one that stays text.
The role "Analyst, data" survives with its comma, in one cell rather than split across two. That is the first thing to check in any converted table, and the usual place a Plain Text file goes wrong.
The quotes around Jonah "Jo" Pryce are left as a plain quote character in the Plain Text.