Why is it a good idea to prevent IPv6 in your network?
The IPv6 standard was approved in 1998 and was designed to replace the IPv4 standard.
There are only a limited number of IP addresses available worldwide. One of the reasons for the new IPv6 standard was now a far higher number of IP addresses available. You could also say that you could now assign an IPv6 address to almost every grain of sand on a beach.
Another motivation for the IPv6 standard is an end-to-end relationship. Manufacturers are required to change the IPv6 addresses of devices once a day after the IPv6 privacy extensions (link).