In Tim O'Brien's The Things They Carried, why is it important to specify the weight of the equipment each man is carrying?

Early in his account of his tour in Vietnam, Tim O'Brien provides a detailed description of the equipment carried by each member of his platoon. The Things They Carried refers not only to the physical items, like weaponry and personal effects, carried by the soldiers with whom he served, but to the emotional baggage as well: the memories, worries, beliefs, etc., that were the provenance of each individual irrespective of those accoutrements issued by the United States Army. In that initial catalog of material items, O'Brien lists the following:

"As PFCs or Spec 4s, most of them were common grunts and carried the standard M-16 gas-powered assault rifle. The weapon weighted 7.5 pounds unloaded, 8.2 pounds with its full 20-round magazine. . .Every third or fourth man carried a Claymore antipersonnel mine--3.5 pounds with its firing device. They all carried fragmentary grenades 14 ounces each."

O'Brien was meticulous in cataloging the full weight of equipment carried by the average soldier in his unit, as well as the personal items each carried for whatever reason, such as superstition or fear ("Lee Strunk carried a slingshot; a weapon of last resort, he called it.") O'Brien's emphasis on the precise weight of each item carried by each soldier serves to illuminate the physical burden each soldier endures as he patrols the jungles, hills and fields of Vietnam. By itself, each piece of equipment might not seem to present much of a burden. Cumulatively, and carried on very long foot patrols under the most demanding conditions imaginable, the burden is considerable. And, to reiterate, this represents only the physical burden. As demanding in some ways is the emotional and psychological burden carried by each soldier. Memories of loved ones back home, for example, or professional careers seriously and, in some instances, permanently interrupted, along with the constant fear of impending violent death and everyday struggles with sickness and heat and mosquitoes all combine for a truly horrific picture of the situation into which governments put their young men and women in support of sometimes ill-defined foreign policy objectives.
O'Brien chose his title quite deliberately. The Things They Carried, both physical and mental, both united and separated the men in the author's unit. The commonalities, such as the weapons and rations, are contrasted with the internal differences that defined them as individuals. O'Brien includes the details on the weights of the physical items to illuminate the burden under which each and every soldier struggled to survive.