Dual talent specialization used to be an expensive upgrade reserved for players with good money management. As time has passed since its inception, its level requirement and cost have decreased dramatically. Everyone can afford dual talent spec now, and the benefits are easily recognized for hybrid classes. What once was a 30-minute trip to a capital city to respec between roles has become a short cast that can be performed anywhere. Pure DPS classes can still use dual spec to their advantage, and rogues are no exception.
I'm going to be honest and tell you that subtlety is still not competitive in PvE. While its unrivaled survivability does come in handy on a few heroic encounters, its damage output is simply not strong enough to warrant regular use. Combat and assassination are our two most potent talent trees, and so most rogues will be sporting these specs in raids. While assassination still holds the DPS crown on most encounters, combat's Blade Flurry can be useful for dungeons and even raid bosses like Halfus Wyrmbreaker. By properly planning our rogues, we can play both specs with a deadly efficiently.