So if ipv6 is not supported on your network infrastructure, it might be useful to disable it all together. Why ? It can cause issues like delayed domain lookups, un-necessary attempts to connect to ipv6 addresses causing delay in network connection etc.

Source: How to disable Ipv6 on Ubuntu, Linux Mint, Debian (BinaryTides)

(This is also applicable to a Raspberry Pi running Raspbian, or some other Debian derivative such as RasPBX)