No, it's better to use the rune for a howling blast (or soul reaper). If you have an unholy rune available already, then it's good to use a frost or death rune for obliterate. But don't hold on to them.
Hi, I recently re-spec'd my alt DK to frost and was wondering if you always leave 1 death/frost rune available when you have an unholy rune up for obliterate when playing DW. Thanks! (playing blood tap)
Not only is howling blast a stronger attack in terms of damage per rune, holding on to resources interrupts our resource feedback loop. When you spend runes, you gain runic power. And when you spend runic power, you gain runes.