You can use it if you want to give discounts at certain events to attract customers to buy your product. Example: Christmas Sale, Ramadhan Sale, etc.
I. Adding Discount All Products Promotion
Step 1. Go to Promotion Menu then click promotion event tab and click add button

Step 2. Fill in promotion event form then click submit

Step 3. Discount all products promotion successfully added

II. Using Discount All Product Promotion
Step 1. Go to sell menu and then input product you are selling, then click promotion.

Step 2. Select active promotion you want to use

Promotion applied successfully :

Step 3. Click pay button to process the transaction

Video Tutorial Promotion Discount All Products
You might also like to read these articles below:
To make a promotion tiered, you can check this article How to Use Promotion Tiered
To make promotion the cheapest item, you can check this article Promotion Cheapest Item
To make a promotion with minimum spending, you can check this article Promotion With Minimum Spending Get Free Gift
To make a promotion discount for specific products, you can check this article Promotion Discount For Specific Products
To make a promotion Buy 2 Get 1, you can also check this article Promotion Buy X Get Y or Buy 2 Get 1