Hi
The original question was:
Does anyone know of the top of their head what duty/privilege is associated with allowing discounts on quotes

However this seems to not be the case. The duties and privileges seem to be fine and this issue is occurring with the Admin user as well.
To update this issues what is happening is every time an item is selected on the line on a sales quote, when that line doesnt have a sales price associated with it then you can enter the discount amounts, However when the line gets filled automatically with a price then the discount fields on the line get locked. The only place where you can enter the discount is in the line details tab > Price and discounts, however a lot of it is greyed out. We dont see this on UAT as everything is available to fill in.
Below is a picture of the line details in production for a quote

Thanks