From farming The Countess over rushing Characters for the Hellforge Quest to the farming of high player count areas which contain monsters with a particularly favorable drop tables. There are several ways on how to farm Runes. A Ber Rune has the highest value among all Runes.
In these combinations, they can be traded for Mid to High Runes. Most of them have close to no value, however, some Runes in this range are frequently used for Runewords or Crafting and can become valuable in the right combinations and quantity.
Due to the rarity of the Mid-High Runes and their numerous uses, they are considered valuable and therefore a worthwhile currency:
A very common use for Runes is trading in Multiplayer.