i figured out what detonate does and just let me say first it is useless. Ok say you use something like heck hound or dragon both have an over time effect right. well detonate takes that over time damage and makes all the damage that would have been done over that 3 rounds and turns it into just 1 turn of full over time damage.
Detonate takes a Damage Over Time spell (DOT) and grants all the damage it would still give over time immediately. I think it is only worthwhile in PvP and maybe not even for that.
Example 1: I go first in PvP. I build pips and send a Heckhound at him. The first round of damage happens. I still have 2/3 of the spell damage to deal to my opponent over the next two rounds, but I use Detonate instead. Detonate destroys the DOT and grants the entire amount of remaining damage immediately, instead of over the next two rounds. This could be handy, for example, against an opponent who is planning to use triage. By detonating the DOT you get all the remaining damage immediately. So if your opponent did cast a triage, there is no more DOT to stop, because you detonated it.
Example 2: I just thought of this one, but I could see where detonate could help in team PvP, if you have two fire wizards, or one fire wizard and another wizard using their DOT spell. The first wizard casts the heckhound. The second wizard casts detonate right after. You get the full damage of the heckhound immediately and your opponent has no time to try to stop it.
It seems to me some of the new spells are geared strictly toward PvP and are not helpful for regular questing.
For stragetic spells like this, try not to over think it, it's very simple if you just follow what it saids and use trial and error. Heck i didn't even know what it did at first until i looked at it closely.