An example what the Legacy system will do for you:
After one of your characters completes Chapter 3, that character gets to pass on a special ‘Heroic Ability’ to all the characters in his Legacy. Powerful Sith Warrior in your Legacy? His Jedi children can "Force Choke" enemies. Father was a high ranking Imperial Agent? Call in some old favors and request "Orbital Strikes" from Imperial warships. Your sister is a notorious Smuggler? She taught you that… special… kick that only Smugglers know.
I couldn't help but laugh about that... special....kick! It appears our basic class buffs we do will be bolstered by the other characters we get to 50. So say I'm on my BH and I cast my stamina buff on everyone, it will also apply the sith warrior's might buff as well since I'm level 50 on my juggernaut. Food for thought since we all have some smidge of alt-itus we like to play out. The family tree information is very interesting and I can't wait to waste hours on it trying to figure out which way I want to go with it.