What XML is
XML marks up data with nested named tags and optional attributes. It is verbose, strict about being well-formed, and can carry a schema that says what shape a document must have.
Enterprise integrations, government data feeds, RSS, SOAP services and older document formats.
What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What changes when you convert XML to Excel
The first repeating element is treated as the rows. Attributes are read alongside child elements and prefixed so they do not collide with a same-named tag. Nesting one level deep becomes dotted column names; deeper structures are kept as text.
You get a single sheet with a header row and column widths sized to the content. Values are written as text unless type inference is on, which keeps identifiers like 0044 or 007 intact.
What carries over from XML to Excel
One property of the XML has no home in Excel, and it is worth knowing which before you convert.
Excel wants a type for each column, and XML does not record one, so each column is typed from what its values look like. A column of digits that should stay text - a zip code, a phone number, a leading-zero id - is the usual thing to check afterwards.
XML can hold a value that is itself a list or an object. Excel has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
The keys stop being repeated: Excel writes the column names once at the top, so the same table takes noticeably less space.