Plastic, being flexible and easily molded, not only uses its unique characteristics, but also can reduce part count by designing a spring as part of another part:
Pressed or molded parts
Pressed metal flanges and tabs increase the precision of insertion and may help reduce part count.
Before
After
Injection-molded buttons or signs
Injection-molded buttons or the keys on a computer keyboard are a good example.
By molding the letters into the keys, they don't wear off like paint or decals would, and the decal application step is eliminated.
Decals, however are desirable where they would not get a lot of wear, because they are less expensive than injection-molded signs.
