I'm not one for more bureaucracy, but I could see how ONE person might be needed to cut through inter agency rivalries, etc. The CIA is, after all, not SUPPOSED to work internally, so they have to share with the FBI. Same for military- they're not in theory a law enforcement agency.
And I don't even want to think of what will happen to our constitutional rights. Can you imagine what would happen if another Clinton-type made it to the top (like Hillary, for instance)? The potential for abuse is truly alarming.