Microsoft Word offers several options for setting the margins of the document you are editing. In addition to normal page margins, you may have noticed settings for something called "gutter margins." When you switch gutter margins on, Word adds extra space to your document's existing margins to allow for the document's binding.
Gutter margins are designed to add more space to the normal margins of a document that will be bound together; this ensures that none of the text will be obscured once the binding is in place. Even if you intend to just staple your document together, or place it within a temporary binding, adding a gutter margin will give your finished document a more professional look and ensure that readability is preserved.
Gutter Margin Position
Word typically allows you to choose whether to position the gutter margin of your document at the top or left of the page; if you have previously set your document to the "mirror margins," "book fold" or "two pages per sheet" layout options, Word will automatically set the gutter margins to a position that matches the chosen layout.
Gutter Margin Width
When setting a gutter margin, allow for enough width to ensure the page layout looks even and balanced. If you are unsure what width to use for a document you will be binding yourself, print out a copy of the document on scrap paper and bind it temporarily to determine how much space the binding occupies; if you will be sending your document to a professional binder, contact the binder and ask what width the gutter margin should be.
Gutter Margins vs. Normal Margins
Although you may also allow space for binding the document by adjusting the top or left margins manually, adding gutter margins is a more efficient way of performing the same task. If you adjust a normal margin to accommodate for the binding, you will have to recalculate the margin yourself every time you want to modify the width of either the margin itself or the binding; using the gutter margin option in addition to normal margins will allow you to change the width of margins and binding independently, without having to perform additional calculations.