The Distribution tab decision screen is used to enter your retailer margin and sales promotion support budgets for each retail channel.
Sales Promotion Support
If your products are struggling to increase their distribution coverage, then this it is a way of boosting distribution coverage by supporting retailers to promote your products in their stores.
The amount of money that retailers receive is equal to the sales revenue they get from your product multiplied by the retailer margin you have set.
Raising your Retailer Margin will increase the number of retailers willing to stock your product given your current sales volume.