The Wilcoxon signed ranks test may be used to test whether two measures from the same sample (ie, dependent samples) differ significantly between them or not. In this case, it functions in a similar manner than the Student t test for two-dependent-samples, except that it is a nonparametric statistic.
The Wilcoxon signed ranks test may also be used as a one-sample test of location. Its parametric counterpart is the one-mean Student t test (From Encyclopedia of Measurement and Statistics).
The underlying assumptions are that the distribution is continuous and symmetric.
Because the Wilcoxon test is a nonparametric statistic, it reduces the likelihood of making a Type I error (i.e., the false positive rate).