Final answer:
Copying layer effects from one layer to another typically overwrites existing effects on the destination layer. This action may result in the loss of unique effects that were present only on the destination layer.
Step-by-step explanation:
When you copy layer effects from one layer to a second layer that already has effects applied to it in a program like Adobe Photoshop, the new effects will overwrite the existing effects on the second layer. However, some software may provide an option to append the new effects alongside the existing ones, depending on how the copy-paste action is performed. If the second layer has unique effects that are not present on the first layer, those effects may be lost unless the software supports merging or stacking of effects.