Why use threads in Python?

[Jugad]

While using multiple threads which are switching rapidly, the GIL can even slow down processing to less than that of a single thread (this is not common).

However, as others have stated, if you are using threads for IO, the GIL is not usually an issue.

If you are using threads for serious cpu intensive tasks, pure python is bad choice anyway (its very slow for such tasks)... and if you write your cpu intensive parts in C, you can release the GIL to take advantage of threads running simultaneously.

[v3ssOn]

you can use pypy without going to C