Tarp shelters are great. But to me, it's a complete no-brainer: No door = no good, in my opinion. There are many tarp shelter designs that do provide a door, at little or no weight penalty. There are many such shelters, however, that are designed with an open front with no option for closing it down.

Among the best-known that don't offer a door would be the "Squall Classic" or Henry Shirer "Squall." [EDIT: statement is apparently incorrect. My current belief is that Shirer shelters previously had no doors but currently have doors.. Sorry for mistake.] Mountain Hardwear briefly made a nearly identical design it called "Batwing" [No door.] which I continue to own, though only rarely employ.

Previously, I used it for quite a few nights, including nearly a week in which there were a series of heavy summer thunderstorms, or "squalls," & during which I became objectionably damp.

My version was designed for two people, but I was alone and able to schrunch myself into middle of this tent. Yet there was plenty of wet that sprayed itself on to me and my gear. It was quite unsatisfactory after a day or two, and and unnecessary, had I used a more suitably designed shelter. A door on Batwing would have added only a few ounces, especially if made of latest silicon-treated nylon.

I have three other tarp tents that have integral doors-- two of them have zippers and one, the SilShelter, has a door that is indescribably primative, but a door at least, nonetheless. I've used all three in four seasons. Wouldn't think for a second of using Batwing in winter. And it's heavier than all the others (Mt. Hardwear goes in big for durability.)

Years back, I relied on a rectangular tarp for many, many nights over a period of years.. Eventually, I obtained the knack of setting it up in a pyramidal configuration in which it could be completely closed to the elements, though resulting shelter was rather small, relative to size of tarp, unless I used supplemental "door" in the form of a poncho (even more complex.)

With this method, I used the simple tarp on a fair number of nights in winter and in some fairly significant snow storms.

It's a slightly esoteric skill which I've now mostly lost. But it can be done efficiently, or at least effectively. The "Squall" and many similar designs cannot be used in this manner.