Chronic muscle tension inhibits circulation, which means your muscles (and other tissues) aren't receiving the nutrition they need. The lack of nutrition and buildup of waste products irritate nerve endings, resulting in weakness and pain.
Chronic muscle tension also inhibits movement. Movement is accomplished by paired groups of muscles alternately contracting and lengthening to move the bones to which the muscles attach. Chronically tense muscles disrupt the symmetry of balanced forces acting on the skeleton, holding bones out of position and causing misalignments. These misalignments cause pain. For every chronically tight muscle, it's opposite muscle (the antagonist) is chronically stretched and weak. This imbalance can increase the likelihood of frequent pain/discomfort and injury over a period of time.
Massage is a great strategy to decrease chronic muscle tension and reduce the discomfort it can cause. By maintaining your body with decreased chronic tension you are paving the way to a more efficient body along with decreased pain and increased energy.