reductioninsm is a worldview, currently in vogue, attempt to break a system down to its component parts. then study those component parts and forget the whole system. for example, in modern medical science , people study parts of the body e.g. heart, lungs, liver, kidney etc. but they do not study the system as whole. in reductionism people are specialists, not generalist. there is a danger in this approach.
it is very much unrealistic approach. in it, you can't predict what will be the impact on the whole system of something you have done on a part. for example you can't say what happen to the body if you do something in kidney or liver because you do not know all the parts and the relation among them. so you in the process of solving a problem will create a new problem.
another example of danger of reductionism is : industrial revolution may solve your financial problem but it creats a global worming problem since you don't know the entire system and relation between the parts.you can't predict that noxus fums emitted from your factory may damage the ozone layer because you only know the factory and you don't know the nature of air and existance of ozone layer and the relation between air and ozone layer.
holism on the other hand considers system as a whole. it will not create new problem in the process of solving an existing one. so i think holism is better than reductionism.