What is the significance of a structural and geometric isomer, as well as an enantiomer?

Isomers have different properties for example, cis-1,2-dichloroethene boils at 60°C while the trans isomer, trans-1,2-dichloroethene boils at 48°C. cis-1,2-dichloroethene has a dipole moment of 1.85 D while the trans isomer has no dipole moment because of symmetry. Also the way the molecules are positioned may affect how they react.
Another example of the importance of cis/trans isomers is in human vision. The compound 11-cis-retinal is located in the retina of the eye. When 11-cis-retinal absorbs a photon of light it is transformed to 11-trans-retinal which causes the shape of the protein molecule that it is attached to change. The change in shape of the protein molecule triggers a sequence of events that generates and electrical signal which is sent to the brain and this is how you are able to see things of all kinds of different colors.
So anyways, isomers are important because of their different properties.