The variations might help the organism to survive if there is a change in its environment
Eg heat resistant bacteria
The variation might help the organism survive predators
Eg. Green beetles blend with green leaves thus disabling crows to spot them
:)
There are so many examples for that in different areas, like TPBA experiment carried out in our lab recently.Here's one link: http://www.alfa-chemistry.com/tpba-cas-172285-72-2-item-294462.htm