Sorry. Not yelling at anyone, I just actually found myself asking myself this question the other day, and then I went "oh yeah, duh, of course I should." T12 4pc bonus gives you free focus in different amounts at random times. T13 2pc gives you a predictable, never ending flow of free focus. It's a huge DPS increase and gets you that much closer to getting your T13 4pc, which is appropriately righteous for an end-of-expansion tier set.
Of course, luck being what it is, the LFR runs I did on my hunter dropped conqueror tokens, and the runs I did on my priest dropped protector tokens.