Enterprise Resource Planning (ERP) customization is a major source of concern for organizations implementing or using ERP systems. Customization has been used to explain implementation failures for years. However, the question of which types of customization have negative effects and which types of customizations have positive effects has not been fully explored. Case studies show that lack of customization sometimes causes negative consequences. What is the reason that some customizations are needed while others should be passed by? Using strategic alignment and systems agility as a basis for understanding the impact of customizations, this paper attempts to gain insight into the impacts of ERP customization.