The rain fly is what prevents you from having to break camp and go home if it starts to rain. It fits over your solo tent providing protection from rain, snow and wind. You will be hard pressed to find a waterproof tent for one person so a quality rain fly is essential.  There are two types of rain fly; partial coverage and full coverage. Within the category of partial rain flys there are those that nearly fit over the entire tent and those that only cover enough to keep rain from coming directly in through the mesh windows. A true full-size rain fly by comparison will cover every part of the solo tent and make sure there is no area that is coming in direct contact with precipitation. The ability of a good rain fly to also mitigate the effects of strong wind cannot be overstated. Strong wind can ruin your camping experience just as easily as rain or snow so being able to deflect it is a huge plus.\r