CSV and Excel files both hold tables, but they are not interchangeable in terms of what they can represent. A CSV is primarily data; an Excel workbook is data plus spreadsheet structure and presentation.
CSV is excellent for simple data exchange
CSV is plain text. A row is represented as a line and fields are separated by a delimiter, commonly a comma. This makes CSV easy for databases, scripts and business systems to generate and consume.
CSV is a good choice when the receiving system only needs a rectangular table of values.
Excel is better for a working spreadsheet
An XLSX workbook can contain multiple sheets, formulas, formatting, charts and other spreadsheet structures. That makes it more useful for people who need to inspect, calculate and present the data.
The extra structure also means an Excel file is not as simple to process as a CSV.
The big conversion loss: structure
When you convert XLSX to CSV, you generally select one worksheet's data and write it as plain rows and fields. Workbook formatting, charts and most formulas as spreadsheet objects are not represented in ordinary CSV.
Going from CSV to XLSX can create a workbook shell around the data, but it cannot recover formatting or formulas that were never present in the CSV.
Quick decision
| Need | Use | |---|---| | Import/export between systems | CSV | | Simple table with no presentation | CSV | | Multiple worksheets | XLSX | | Formulas and charts | XLSX | | Human-facing report | XLSX |
Try Excel XLSX to CSV or CSV to Excel XLSX when you need to move between the two.
Bottom line
Choose CSV when portability and simple data exchange are the priority. Choose Excel when the spreadsheet itself—not just the values—is part of the deliverable.