It is no longer news that Paypal is the largest and most secure Payment platform the world has today and so not having it as a payment option is directly keeping a larger portion of your visitors away.
When you have an e-commerce application, it is essential that you have a user-friendly mechanism for payment.
While e-commerce sites will typically use complete credit card processing gateways, when you offer PayPal as a payment option for customers it can be beneficial. For example, there are some who do not want to send their credit card info across the internet and this integration will eliminate the need for this.