Obviously, when we are out on the trail, the reason we bring these types of insulation is their ability to compress and fit in our pack and so compressing them is a necessity. However, the loft we use to keep us warm is created by the fibers acting like little spring, holding up the loft. If a spring is left compressed, it loses some of it’s ability to do this. Different materials react differently to this. Synthetics typically will suffer the effects of compression much more than down, which is very resilient to compression. However, it too is like a bunch of little springs that inevitably will react to compression cycles and long term compression. You’ll hear tales of “I leave my down bags smooshed in compression sacks for years. Pull them out and they’re fine!”. Well, they may seem fine, but it’s likely due to the overstuff making up for some loft loss. Maybe it’ll be noticeable, maybe not…but you can be sure that every compression is some level of a dent in it’s ability to loft. So, it really makes the most sense to only compress your insulated items as small as you need, for as long as you need. If you have room in your pack, no need to smash your sleeping bag into a tiny compression sack. Let it fill the space and give your pack structure too.
When you set up camp, take these items out and tend to them. Move the down around in the chambers a bit by patting, then let them sit to loft up. Then distribute the fill as needed before you crawl in for warmth. If you have a horizontal chamber system it usually makes sense to grab the underside of the system and shake the fill towards the center of the chambers, which will be the top of the system when you are in it.