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 CSV is
CSV is a text file where each line is a row and commas separate the fields. There is no type system, no formatting and no second sheet. Every value is text until something downstream decides otherwise.
Almost every database, analytics tool and spreadsheet can read and write it, which is why exports default to it.
What changes when you convert QIF to CSV
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.
Any value containing the delimiter, a quote or a line break gets wrapped in quotes, and embedded quotes are doubled. That is the rule in RFC 4180 and it is what spreadsheet software expects.
What carries over from QIF to CSV
One property of the QIF has no home in CSV, and it is worth knowing which before you convert.
QIF distinguishes a number from the text of a number; CSV does not, so every value arrives as text and has to be re-parsed by whatever reads it next.