If the hops are floating a certain percentage might not be in contact with the wort. Weighing them down just ensures that they are all covered.I'm dry hopping at the moment, I often do it without a bag but have started using one the last few years, just chucked in.
Is there any proof that weighing the bag down makes a difference or is it just another one of those brewing rumours that perpetuates?
If you’re using a plastic bucket for fermenting you can just throw hop flowers in - they will float on top and will still be floating on the top several days later but now they will be big and fluffy.I'm not terribly into hoppy styles anymore so I don't dry hop, but it always caused a lot of trouble. Often found it difficult to sink the bag, and when it floated on top it would get infected and ruin the brew on occasions. If I DH with pellets or whole cones loose they would end up in my bottles. Now I have a fermentation fridge I'm considering dry hopping a beer and drying out leaving them in loose and cold crashing, seeing if that sinks all matter to the bottom.
Or free with a Festival kit, assuming they still provide them, thats where mine came from.A syphon with a small drawstring net sock over the end will allow you to draw off clean clear beer with no bits. I use these on the end of my syphon: