When Second Wind is cast without any exhaustion, it provides only nine energy, due to exhaustion recovery during the two second activation time (netting +4 total).
Increasing exhaustion to more than half of total energy is fairly wasteful, as more energy is gained than the character's maximum energy (and the excess energy is lost). It is generally best to aim at keeping the total exhaustion between 1/3 and 1/2 of the total energy.
In order to use Second Wind efficiently, it is best to have at least 70 maximum energy.
A major disadvantage of Second Wind is how much exhaustion is required to really benefit from it. Recovering from 35 exhaustion takes 105 seconds. This may require entering future battles with lower than maximum energy, or long waits between battles.
Exhaustion may be built quickly by using the skill and interrupting the cast right away (with the Escape key, or moving during the cast (movement buttons or mouse clicking, both work)), several times on end.