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 TSV is
TSV is CSV with tabs instead of commas. Because tabs almost never appear inside a value, quoting is rarely needed and the files are easier to read by eye.
Bioinformatics, log processing, and anyone who has copied a block of cells out of a spreadsheet: the clipboard format is TSV.
What changes when you convert YAML to TSV
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.
Pick TSV over CSV when your values contain commas. Pasting the result straight into a spreadsheet fills the cells correctly with no import dialog.
What carries over from YAML to TSV
YAML records 4 things about a table that TSV has no way to hold.
YAML distinguishes a number from the text of a number; TSV 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 TSV, 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. TSV 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 TSV, so line breaks are replaced rather than carried through.
The keys stop being repeated: TSV writes the column names once at the top, so the same table takes noticeably less space.
The result can be read a record at a time, and appended to by adding to the end of it. That is worth having for a table too large to hold in memory, and it means a TSV file that is cut off part way through still gives you every record before the cut.
The identifier 007 comes out of the TSV 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 TSV file goes wrong.
The quotes around Jonah "Jo" Pryce are doubled, which is how the delimited formats escape a quote in the TSV.