What MySQL Output is
Not a file format at all. It is what the MySQL command line prints when you run a query: a box drawn with plus signs, dashes and pipes, with a line underneath saying how many rows were in the set.
Anyone who has run a query in a terminal and wants the answer in a spreadsheet.
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 MySQL Output to TSV
The rules and the trailing row count are dropped and the pipes become column boundaries. MySQL prints an unset value as the four characters NULL, which arrives here as an empty cell, because that is what NULL means and because a literal string of NULL in a spreadsheet is worse than a blank. Paste it as CSV instead and every row becomes one column full of pipes, which is why this is its own format.
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 MySQL Output to TSV
MySQL records 4 things about a table that TSV has no way to hold.
MySQL 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 MySQL both come out blank and can no longer be told apart.
A line break inside a cell ends the row in TSV, so line breaks are replaced rather than carried through.
TSV has no separate idea of a header, so the column names become an ordinary first row and nothing in the file marks them as different from the data.
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.