With SLAAC, your MAC address is embedded into your IPv6 address. When you connect to the world, you’re giving them something that can be traced back to you (or at least a piece of hardware you have). RFC3041 was created to help address this privacy issue. It’s since been obsoleted by RFC4941.
Read more in the article of IPcalypse how to enable this on Ubuntu (which will probably work on other Linux flavours as well)