
A 12 string guitar is very much like a 6 string version, but of course, with more strings. Essentially, each string is effectively doubled, which has the effect of creating a very unique sound. It is the natural equivalent of using a chorus effect.
The 12 string guitar is most commonly used as a rhythm instrument. The close proximity of the strings and the higher string tension make them largely unsuited for lead playing. This is mostly due to problems with picking and note bending.
Because the string tension is much higher on a 12 string than on a standard 6 string, these instruments are prone to warping issues. Many manufacturers try and solve this problem by incorporating additional bracing and support. However, in most cases, even the most robust models will eventually have problems.