There is a common opinion that personal data should be deleted almost immediately and, anyway, as soon as they become useless: a sensitive problem in particular under the (now defunct) Data Retention Directive, once the mandatory retention period expired.
This position is not correct since a company has a legitimate motive – and a legal obligation – to preserve whatever information, including personal data, that are necessary to abide the law and to protect both its right of defense and the right to a due process. This means that under the term set forth by the Statute of limitation a company might, at its own will, choose to continue retaining personal data of its customer base.
In Italy, the ordinary Statute of limitation is ten years. So companies can be sued by customers and tax authorities for alleged charges that go way back into the past. This is what happened in a court case tried in front of the Justice of peace of Grosseto (Tuscany) that on January 2014 ruled a quarrel started in 2011 between a telecom company and a client. The ruling said that, under the rule of evidence for civil trials, the telecom company has the duty to provide evidence of having actually delivered its services and that this duty is fulfilled by showing the traffic-data log.
It is clear that by interpreting the Italian Data Protection Act in a way that forces the deletion of the traffic data after a few months, an ISP or a telecom operator wouldn’t be able to defend itself if the trial starts within the Statute of limitation term but after the traffic data have been deleted.
A similar situation might happens in the antitrust field and in case of investigations run by the Italian Internal Revenue Service, so the conclusion is that the Data Protection Legal Framework cannot be interpreted in such a strict manner to endanger the legitimate rights of a company.