While leathers are typically joined via methods including sewing or riveting, sometimes it can be helpful to first secure the surfaces with a glue or adhesive. Once in position, it makes it easier to do the sewing, riveting, etc.
There are many different types of adhesives available that work well with leather. Some are temporary, with a tacky result that can be easily moved and reapplied. Others are stronger and more difficult to remove. Some glues expand into the materials as they dry. And yet others are extremely strong, considered permanent. For very strong glues, they bind so tightly that trying to remove the adjoined pieces will likely damage the leather.
Wool daubers can be used to help apply and smooth out leather glues. It’s important to know the preferred end result. If you plan to remove stitching at a later point and separate leather pieces, consider using a less strong, or temporary adhesive to make this easier. Glues are available with different drying times, and some variations in colors.