Imo Level 2 of Advanced Haki is to use your Haki outside of it's Original Limit,
In other words,
Level 2 CoA (Barrier) allowed User to let their CoA flow beyond their Bodies,
Level 2 CoO allow User to let their CoO include more than just their own Senses (Telepathy) as used by Kata, Yasopp, Zunisha ... etc
Level 2 CoC allow User to let their CoC include more than just themselves,
For example, when Shanks used CoC on Ryokugyu, He also included his Crew,
Such Ability allow you to both use your CoC through others (Like imagine Chopper is walking, gets surrounded by Enemies, and then Luffy unleash his own CoC from Chopper's Body) and also allow you to include other's Haki, making your CoC Coated Attacks on a completely whole other Level & They basically Scale to Infinity (After all, a Conqueror is like a King, so it makes sense that the Bigger/Stronger your Kingdom, the Stronger you also get),
However imo, only someone who learned Hardening can eventually learn Barrier,
And only someone who learned Future Sight, can eventually learn Telepathy,
And only someone who learned CoC Coating, can eventually learn this CoC Sharing Ability, (It's like Haki Version of Faith)