What is Desire?
The most powerful emotion in my opinion is desire. Desire is the most powerful since it is the logic that governs everything. So just think about it for a second, everything you do in life a based on a want and a want is in fact a desire. Thus if you want a better job you in fact desire a better job. Desire is even the basis of love since before you can love someone most of the time you have a lust or want to be with them aka a desire. Love in essences is the desire to be happy with one someone no matter anything else or connect with someone on higher level when compared to anyone else.
The effects of desire:
Of course too much desire can lead to evil/negative things. One such example is the rebellion from the bible, in which desire in was the basis for all that happened. When looking at the seven sins most of them can be summed down to an overpowering form of desire, as well as some of the virtues. Yet desire can also lead to an extreme level of good or kindness. One such example is Jesus, who had a desire to change the world for the better. But this to can be negative for one person's desire to help can be mutated into another desire for power. Such is what happened in the early church were the Roman senate debated which books to put in the bible. The books they choice were the ones the ones that made Jesus look like a god not a man even though those books were written years after some of the ones that made Jesus appear simply as a man. Later on desire for power lead the church to have inquisition. Until the point where people were so blinded by faith that they killed anyone who didn't see the world the same way as them. The unfortunate fact about this is this seems still to continue today with Christians, Muslims and Jews. Another effect of desire for power in religions is how one religion demonizes the god (s) and holy figures of another to gain power.
The uses of Desire:
Desire can be very useful for psychic trying to gain a grasp on their abilities or get stronger. From personal experience I have learned that if you truly desire something/anything it will happen. For example if you focus on astral projecting long enough it will happen. The only problem with is completely desiring something is you must want it with every ounce of your being to have it happen and to do that takes patience and time but once you reach that point. It is easily accomplished again.
So basically, I'm saying if you want to understand or use your powers you must desire to. But be careful using it and aware of the consequences of using it otherwise it can and will consume you.