A Greater Adventuring Kharmic Line creates a situation where your PCs are each individually a manifestation of a single 4D being. Each PC is a single facet of that being, and as such , on a subconscious level shares a group mind.
AN EXAMPLE of actual play ( prob the easiest way of explaining)
In my long running Mysantia game(31 real years), The Kharmic Line was the immune defense system of the 4D being that was the "brain " of the prime material plane. The PC's , from even the lowest of power levels, are tasked with dealing with threats to the prime material plane or Vivvar.
As the PCs are all individual facets of this immune system, they share certain advantages. They have complete access to the the shared memories of the Kharmic Line facets of the past, going back thousands of years. This is due to the immortality of the Kharmic Line itself. All PCs retain all knowledge of their prior characters and all knowledge of any specific game material, rules and background. The net effect of all of this is it totally and completly explains the meta game and makes it basically go away. You can handle this to degrees. I usually allow the players information actually contained in their own brains, not accesses to game books during play. Kharmic Memories can be introduced as needed and desired. Another advantage is that the PCs can separate physically and can then easily find each other again. In fact it is impossible for the PCs to separate for long periods of time(not more than a day or two).
WHY YOU SHOULD USE THIS
Very simply it is the absolute end of meta game. It also forces greater cooperation of the group as they share the subconcious group mind and are in fact parts of a greater being. This only should be taken to the extreme of the group MUST share the overarching goals of the 4D being WITHOUT impacting individuality in character creation and execution.
TAKING THIS TO THE EXTREME
The 4D being the PCs represent carry over into all games and genres that your group plays. I have not gone this far.A nice addition to this would be that all the characters of a single player share one small in game bonus and one small quirk, both should be small but noticeable.For example, always wears yellow, always has red hair always has slightly superior eyesight.
OTHER FORMS OF KHARMIC LINES
The only other one I used with any regularity was the Sagacious Kharmic Line. It represents individuals driven to the extreme need to provide information to the Adventuring Kharmic line. Most of the NPCs who were subject to this chaffed at their burden and deeply resent their lot in life.