Mutations in an individual or population are necessary for adaptation to the environment, which is the driving force behind evolution. Without natural mutations, living organisms would not progress or evolve as a population in response to variable environmental stimuli.
Mutations typically favor a small subset of a population rather than the majority, which often causes evolutionary bottlenecks that change the gene pool of the species in question. For example, a population of rabbits may have many different mutations governing fur colors and patterns. The significance of this variability is that the colors and patterns that best blend in with the rabbits' environments will be passed on to the next generation because the rabbits with more ostentatious coloring will be easily identified and hunted by predators.
Any mutation can allow for an individual to have an advantage over other members of the species. A mutation could make an individual more camouflaged to avoid predators, faster to catch prey, hardier to withstand environmental stress, or even better equipped to utilize nutrients. At the same time, some mutations can be a deficit to individuals, as is the case with genetic disorders such as multiple sclerosis. In general, mutations in an individual organism can either help or hurt the chance that the individuals' genes will be passed on to progeny.