By using the Minimum Weight and Weight Applies To fields you can restrict when Freight Rate is displayed. It is best explained by example.
If we want Freight Rates to be shown only when the weight in cart is over 100lbs then we set Minimum Weight to 100 and Weight Applies to to ORDER. Restrict Rates will be set to TRUE. This will result in only Freight Rates being shown when weight is over 100lbs. If Restrict Rates is set to false then over shipping rates (e.g. UPS) will still be shown alongside Freight Rates.
It will be possible to apply a minimum weight just to an individual item, these feature is not currently implemented.
The YRC freight extension allows you to apply percentage discounts on returned freight rates. To apply discounts you simply need to navigate to System > Configuration > Shipping Methods and from that page look for your Webshopapps YRC Freight extension.
Amongst the configuration options for the extension, you will find a field that says Apply percentage discount. In this field, input the percentage discount you would like to offer all your customers on their returned freight rate and the extension will calculate the discount and apply it to the rate when the customer requests a quote.