Snap buttons have several useful applications:
Temporary fastening
Snap buttons are often used for temporarily fastening tow pieces together that are meant to be easily separated. Things like closures on bags, pouches, lunch boxes, etc. Snap buttons provide an easy to use snap closure that can securely close and reopen the items.
Decorative accents
Snap buttons are sometimes used as decorative accents or closures on clothing, accessories, crafts, etc. The snapping closure provides an audible “snap” that can be an attractive design feature. Things like snap closures on jeans pockets, snap tabs on bags or purses, etc.
Name badge holders
Snap buttons are commonly used to attach name badge holders or lanyards to shirts, jackets, bags, etc. The snapping closure ensures the badge holder stays securely attached while still being removable.
Utility closures
Snap buttons provide an easy to use mechanical fastener that can be used for various utility purposes. Things like closing compartments or pouches on tool belts, sport equipment, pet supplies, etc. They provide a strong closure that does not require tying or other locking mechanisms.
Temporary repair
Snap buttons can sometimes be used for temporary repairs or fastening together torn seams, ripped straps or other separations on clothing, bags, tarps, and other fabrics or materials. They provide an easy solution until a permanent repair can be made.
Craft projects
Snap buttons are useful for various DIY craft projects. Things like creating photo covers, attaching ribbons or string to packages, creating closures for boxes or baskets, and more. Their snapping closure works well for many craft and decorative purposes.
Those are some of the most common applications and uses of snap buttons.