Deduplication is crucial for several reasons. Firstly, it helps maintain a clean email list, which can improve deliverability rates. Duplicate emails can lead to higher bounce rates and spam complaints, negatively impacting your sender reputation. Secondly, it can save costs by reducing the volume of emails sent, particularly if you are using a service that charges based on the number of emails sent. Lastly, it enhances the customer experience by preventing recipients from receiving multiple copies of the same email, which can be annoying and lead to unsubscribes.