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 JPEG is
A lossy image format designed for photographs, where losing a little detail in a gradient is invisible.
Places that will not accept a PNG upload.
What changes when you convert Excel to JPEG
Only the first sheet is read, and cells are read as the text Excel displays rather than the number underneath. That matters for dates: a cell showing 15/03/2026 arrives as that string, not as a serial number you would then have to decode.
The same render as PNG, saved as JPEG. It is the worse choice for a table and it is worth knowing why: JPEG compresses by discarding detail around sharp edges, and a table is nothing but sharp edges. Letters get a visible halo and hairline rules blur. It also has no transparency, so a background colour is always painted rather than left clear.
What carries over from Excel to JPEG
Excel records 4 things about a table that JPEG has no way to hold.
Excel knows which of its values are numbers. JPEG keeps only their appearance, so nothing downstream can sort or sum them without someone reading them back off the image first.
An empty cell and a missing one are the same thing in JPEG, so a null and an empty string in the Excel both come out blank and can no longer be told apart.
Nothing in JPEG records that the first row is a header. It is drawn at the top and looks like one, which is all that is left of the distinction.
JPEG is the end of the line for this data. Reading the table back out of it is a separate and much harder problem than writing it, so keep the Excel if you will need the values again.