Many sanding blocks and finishing sanders are designed to use a quarter sheet of standard size sandpaper (8-1/2"x11"). Some woodworkers will cut the sandpaper into smaller pieces. Another option is to fold the sandpaper, rotating sides as it wears. If the sandpaper is folded so that two abrasive side touch, the paper will wear against itself during use.
To prevent this it is important to fold the paper so the abrasive sides contact only the non-abrasive backsides. This fold requires a single cut along ½ of the sheet. Using the folding procedure shown below you can use a full sheet without premature grit wear.