They make the loading of bait onto the feeder extremely quick, due to the flexible plastic it is make from.
Using a mould will make your casting a lot more accurate
By using a mould you will place your hookbait in the ideal position amongst the bait on the feeder
This mould will work with most flat method feeders on the market
http://www.matchtackle.co.uk/guru-x-press-method-mould-post-free.html