Great question—this is one of those weirdly undocumented edge cases in the Excel Interop API that can trip up even experienced developers. Let’s break it down clearly:

First, let’s look at the method signature for Microsoft.Office.Interop.Excel.Workbooks.Add():

Workbook Add(object Template);

The Template parameter is optional, and it’s designed to accept a few different inputs:

• A file path to an Excel template (like .xltx or .xltm) to base the new workbook on
• An XlWBATemplate enum value (e.g., xlWBATChart for a chart-only workbook, xlWBATWorksheet for a blank worksheet)
• A boolean value—this is the part that’s rarely explained!

When you pass true as the parameter:

• Under the hood, Excel interprets this as a request to create a workbook based on the default worksheet template. The end result is exactly the same as calling Add() with no parameters, or explicitly passing XlWBATemplate.xlWBATWorksheet: you get a single blank worksheet in the new workbook.

You mentioned seeing people use empty parameters or numeric values like 1/2—those numeric values are usually just the underlying integer representations of the XlWBATemplate enum. For example, xlWBATWorksheet has an integer value of -4167, but some developers might use hardcoded numbers (not a great practice, since it’s less readable).

As a side note: If you passed false instead of true, you’d get a workbook with no worksheets at all—this is a niche use case, but it’s useful if you want to build out your workbook entirely from scratch with custom-named or formatted sheets.

To make your code more readable, it’s better to either use the enum explicitly or omit the parameter entirely, like so:

// Explicit and readable
var workbook = excel.Workbooks.Add(XlWBATemplate.xlWBATWorksheet);

// Default behavior (same result as passing true)
var workbook = excel.Workbooks.Add();

内容的提问来源于stack exchange，提问作者jdonnelly