Why disable the garbage collector?

One use for disabling the garbage collector is to get more consistent results when timing the performance of code. The timeit module does this.

def timeit(self, number=default_number):
    if itertools:
        it = itertools.repeat(None, number)
    else:
        it = [None] * number
    gcold = gc.isenabled()
    gc.disable()
    ...

In Python2 and up to Python3.2 gc.disable() is also used to avoid a bug caused by garbage collection occurring between fork and exec. The problem seems to have been fixed in Python3.3 without needing to call gc.disable().