There are evils in the world the overcoming of which can lead to good and self improvement - the struggles that make us brave, loving etc, when we are given a choice by a difficult situation and we do the 'right thing'. Thus there are evils which if they did not exist would reduce the 'good' available in the world.
Anti-theistic philosophers have pointed out there are many evils in the world that are not good for 'soul making' in terms of character or spiritual development. There are grievous evils suffered by those who cannot benefit from them: animals and young children and there are evils - degrees of severe loss and pain and distress that are 'soul destroying' and degrading for individuals, for families and societies, that may tear down and disintegrate with no possibility of resurrection or apparent redemption.
However I think that the anti-theists fail to consider other reasons why the existence of evil may be necessary a) to create creatures at all b) to create intelligent creatures. Firstly, creatures must necessarily be finite in space and time, and so limited. It is difficult to imagine how a finite, limited creature could not be prone to death or destruction particularly if every aspect of creation is in fact in a continual 'process' always existing in an unstable equilibrium between static order and distingegrating chaos. Evolution also requires environmentally caused death and an oversupply of victims to drive natural selection. Apparent free choice and real, sometimes painful consequences of making the wrong choice or incorrectly reasoning fashion our minds toward the correct kind of conduct, and appreciation of our environment, as well as striving to overcome a problem and adapt to a difficult environment drives most human progress.
It is difficult then to see how there can be creatures, and intelligent creatures, as well as truly virtuous creatures if we didn't live in a world where gratuitious evil was possible - a world that is truly free and 'real' not simply a plastic world deforming to our whims and where choices have no real consequences (because evil cannot result no matter what we will)
However I note that while my argument is a 'gain' for a 'soul making' theodicy, the theist is presented with a new problem: if evil is necessary for intelligence etc, how can 'God' be intelligent, good etc if God does not experience evil?