For any hard-disk space issues, which may cause video black out, or computer hang during play. Performing a reset of the game to default may resolve such issues.
To trim to default files only, need to
go into the World of Warcraft folder, and delete the WTF, Cache, and Interface folders.
Another advantage is for easy portable. After deleted those reseting files, the folder will be lean, which enable to copy out to thumb drive or DVD. Which can be use to copy to another computer, or to perform reformat the hard-disk.
The ideas of reseting are reference from: