Benefits of upgrading to latest version (2.1.2)

[eluser]bikuta[/eluser]
Hi guys,

I have a client who is thinking of upgrading to 2.1.2, we built a web app for them way back using 1.6.3.
They're asking for a list of benefits for upgrading the CI framework, I know that I can see all the bugs fixed in the change logs, but do you guys know of any other things I could mention? e.g., performance, security improvements perhaps? if there are any references online that I could use that would be even better.

Thanks!