When you buy something from online, you don't know who the seller. It is not also safe for you to pay him visiting unknown seller.
In those situations PayPalBD is the safest way to make your payment. Because you don't need to visit the seller, even you don't need to know who is the seller. you also don't need to show your sensitive financial information like your bank account number to the seller.
This way, PayPalBD keeps you secure and also make your life easy.