  The WKB approach for finding quasinormal modes of black holes, suggested in
[1] by Schutz and Will at the first order and later developed to higher orders
[2-4], became popular during the past decades, because, unlike more
sophisticated numerical approaches, it is automatic for different effective
potentials and mostly provides sufficient accuracy. At the same time, the
seeming simplicity of the WKB approach resulted in appearance of a big number
of partially misleading papers, where the WKB formula was used beyond its scope
of applicability. Here we review various situations in which the WKB formula
can or cannot bring us to reliable conclusions. As the WKB series converges
only asymptotically, there is no mathematically strict criterium for evaluation
of an error. Therefore, here we are trying to introduce a number of practical
recipes instead and summarize cases in which higher WKB orders improve
accuracy. We show that averaging of the Pade approximations, suggested first by
J. Matyjasek and M. Opala [4], leads to much higher accuracy of the WKB
approach, estimate the error and present the automatic code [5] which computes
quasinormal modes and grey-body factors.
