I've been reading through Water Monkey's blog and some other sites and the general theme seems to be the newb's using very large tarps and as you gain experience/comfort the tarp size seems to decrease. I wanted to throw this out to the group as more of a "discussion".
My thoughts with a tarp are that #1 it is the main shield from the elements and #2 it should provide sufficient protection.
There are a lot of hangers that use the smallest tarps they can get away with, seeing as they are lighter. For fair weather this would be OK, but what about the occasions when you are set up through storms? In a straight rain you will probably be OK, but any wind blown rain is bound to get in somewhere - not to mention the ground below the tarp.
How are you supposed to get any sort of cover over yourself and your gear in the rain, say to dry off and put fresh clothes on, when the only thing that fits under the tarp is the hammock?
My big mamajamba tarp is probably the biggest, or one of, and for space its great. We've even camped under it cooking dinner waiting out thunderstorms. I know weight is a viable concern, but when you need the protection I don't think you can beat having a nice big tarp.