Making expiry dates optional can be performed on a per-Customer and per-Product basis.
Expiry Dates will still appear throughout the application, however, they no longer need to be entered if they're made optional.
Configuring the default for the Customer
By default, all Products are set up to have Expiry Dates turned on/off from the Customer Settings.
From the Edit Customer page, you can disable Expiry Date required? for all of the Customer's products in one go.
Note that each Product then has an option which allows it to either default to the Customer settings or override them for that particular product.
From the Edit Product page.
Changing a Single Product to not follow the default
From the Edit Product screen, you can configure how to handle Expiry Dates: