High tension gives more control, but at the expense of power. Low tension creates the trampoline effect where the ball is is contact with the racket for a longer period of time, deforms the strings more than usual and the strings impart more energy on the ball because of the longer contact time. Manufacturers usually recommend a tension range, and if you don’t know any better, the middle tension is usually a good starting point.
If you are using strings that are designed for more power, the tension should be slightly higher than what you would use with typical touch strings.