XLSX is awkward for scripts, databases and import tools that expect plain text. Arrow is typed and quick for analytics tools to load. XLSX is at home in spreadsheets with formulas, formatting and several sheets; ARROW is the usual choice for passing tables between data tools without conversion cost.
One XLSX can produce several ARROW files; when it does, they are offered together as a ZIP download.
Each column gets one type chosen from all of its values: a column is numeric only if every non-empty cell is a number, and anything mixed, or a value such as a ZIP code with a leading zero, stays text. A workbook with several sheets gives one file per sheet.