What QIF is
QIF is a plain text list of transactions, one field per line, each line beginning with a single letter that says which field it is. D is the date, T the amount, P the payee. A caret on its own line ends a transaction.
Quicken, and the long tail of banks and budgeting apps that still offer it because everything can read it.
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 QIF to TSV
Each block up to a caret becomes a row. Split transactions, which QIF writes as repeated S, E and $ lines, are joined into single cells rather than being spread across as many columns as the most-split transaction in the file has parts. The account type from the !Type header is added as a column.
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 QIF to TSV
One property of the QIF has no home in TSV, and it is worth knowing which before you convert.
QIF 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.