Enabling your potential customers to customize your products prior to purchase you can benefit greatly in the following ways.

Adding value for the customer, for very little or no additional cost. The product purchased goes from something bought to something created thereby becoming more valuable to the customer and instantly sharable on social media.

Customers will pay a premium for customized items (according to Bain customers are willing to pay a 20% premium for customized products).

Customers are more likely to recommend your business / brand. (According to Bain customers given the opportunity to design their own shoes gave companies a 50% higher net promoter score (NPS).

Extend acceptable delivery times for customized products (a study by Deloitte found that 48% of customers would be willing to wait longer for service).

Return rates tend to be lower for customized products, however customers still expect a 30 days return policy.

Differentiate your products and brand from your competitors. Make your customization a USP to increase sales.

Through customer product customization you can spot trends, buying habits that can be leveraged to improve products and / or create new ones. Its all about using data for personalize what you offer.

Build customer loyalty. If customers get what they want then they are happy.  A happy customer is more likely to return and buy again, especially if you make them feel valued.  In addition repeat business is less costly, thus making your business more profitable.

Customization provides a digital extra to market. For example by utilitizing conversion rate optimization onsite you could offer:-

Limited time discount or free customization

Lucky wheel free or discount customization

Free customization when combined purchase value over X amount.

Free customization on exit intent detection

The additional marketing ammunition also works for your email marketing campaigns to provide a convincing upsell.