Totemic Focus, for me, is really valuable while leveling. I'm constantly throwing totems down for a new trash pack or the next set of mobs when grouping. If I am solo and the mobs aren't dying quickly, I am saving more mana there.
When it comes to raids/instances. If I attempt to "Totem Twist" I am going to need that mana as well. Keeping up the Agi buff as well as Windfury for the melee group is really advantageous but also mana intense.
In PvP I'm constantly switch totems for the moment. Grounding totem, and back to windfury for my Warrior partners. Or Earthbind and Tremor Totem. The mana reduction is really important there. Shamans have so much intense Damage while they still have mana. Its a huge gate in getting stuff done. Once I'm out of mana I have to try to retreat to get some more.
Those are the moments where I find Totemic Focus to be extremely valuable.