well bumblebee, it all depends on your humidity level, and what you are growing. like all orchid issues, your location, light, humidity etc need to suit the environment the particular orchid needs. orchids that like to go dry, no moss! orchids that like to stay damp, use moss! but watering is key, and whether you pack tightly or not depends on the amount of moisture you want to retain. mostly you want to figure out what will work in your weather, so whatever will keep the moss damp, without it being soggy. like i said before, the moss should be like a sponge that has been wrung out. wet it, squeeze it... it is still wet, and will hold much moisture, but not be sloppy wet and dripping. then find a way to keep it mostly in that state by adjusting your watering schedule and amount of water. for me, this changes by season. right now i water once a week, but as it warms, it will be at least twice a week. i have experimented over some time to find what works for me, and i find that phals like straight moss, but oncidiums need a mix to be happy, otherwise their roots were rotting on me. also, people use moss for seedlings because they could dry out way too easily, and the moss keeps wet longer than other mixes. same thing with 'sphag and bag' technique for sickly plants. once you have no roots, or few roots on an affected plant, the best way to nurture those roots to regrow is to set the rootless plant on a wad of damp moss and put it in a closed plastic bag, so it does not dry out.