The idea is to get as many relics as possible so you can reforge them into the higher relics. Lots of different strategies being done to accomplish that. I'm not recommending any particular strategy, just providing the info I have come across.
Deconstruction Hints – Heritage Runes won’t appear as a result of deconstruction unless the item is at least level 15. Deconstructing a level 21 Legendary Item opens up even more possibilities, while deconstructing a level 50 Legendary Item can generate a heritage rune with enough experience to level an item to 41 by itself as well as dozens of Relics.