Referencing memory after it's releasing can provide many unfavourable affects: corruption of real data, execution of arbitrary code etc. As a rule, freed memory is distributed to another pointer while the original pointer of the memory gets a new placement and begins to use new resources that leads to problems in system work.
Using of already freed memory can become the reason of current data corruption, DoS crash and malicious input by attackers .The vulnerability is introduced during Architecture and Design, Implementation stages.
Latest vulnerabilities for CWE-416
Description of CWE-416 on Mitre website