Just for ease of set up. Some like to leave their suspension connected to the hammock so as not to forget the tree straps which happens. I personally found having a biner handy for throwing the webbing around a tree I can't get my arms around. I've read that there is theoretically less potential for friction damage but I've not seen many posts about that. If you are good with threading the webbing then you don't really need to add hardware to save yourself 5 seconds.
Don't let life get in the way of living.