Everybody hates waiting in line, so a short waiting time makes customers happy.
Many items on display amount to optionality. Customers love that!
On the other hand, a cluttered checkout counter might discourage customers from even glancing at the display.
Other discouraging issues that must be noted here are:
Image by Arek Socha from Pixabay
Reference: How to Use Your Checkout Counter to Make More Sales by Kali Hawlk on Shopify