It's been done for generations to varying degrees. Believe it or not, career managers aren't just randomly plucking names and sticking them in jobs - there are attempts to get people broad experience, and specific efforts are made to groom and develop folks.
Succession planning is merely a formalized method to develop our institutional leaders. In a 30-35 year career it's impossible to do everything; succession planning helps get people exposure to as many key things as they can, in trade and out of trade, in and out of their home environment.