With respect to this question, is it always necessary to have perfectly concurrent-safe web-application or can a developer afford to let some possible concurrent issues untreated (e.g. when money is not involved) because probability of them happening is very low anyway. What is the best practice?
NOTE: If I say concurrent issues I mean the issues raising from overlapping executions of scripts. I do not mean the multi-user issues like classic lost-update with the timestamp solution cause probability of these things is imho significant and I am pretty sure here that the best practice is to always treat them.