Convection is a passive talent that reduces the mana cost of a shaman's offensive spells.
% Mana Reduction
This is perhaps one of the most useful spells for Shamans who use these types of spells, and compared to [Concussion] would be preferred if the Shaman is concerned about running out of mana during battle. It is strongest to a Shaman investing deep in the Elemental tree, and Shamans who are devoted to doing damage might consider getting both Convection and [Concussion].
PvP Shaman should consider completely passing on this ability, as most PvP fights don't last long enough to need the reduced mana cost. PvE shaman however should consider taking both Convection and [Concussion] as there could be some hard burns which can deplete your mana quickly!