The font preferences allow the user to change the font which is used by default in the Gnumeric grid cells and to set the font used for headers and footers when printing.
The Font selection sets the default font name, size and style to be used in the cells on every sheet.
The Headers/Footers selection sets the font name, size and style which will be used, by default, in the headers and footers added to each page of printed output. These selections can be over-ridden in the print preferences dialog as explained in Chapter 15 ― Printing. The content of the headers and footers is determined via the Page Setup dialog, detailed in Section 15.2 ― Page Setup..