Currently it's possible to shoot without pause for as long as you like, which has consequences on a flow of a firefight, which translates onto an overall experience.
Having a possibility to overheat a weapon would result in more realistic and tactical gameplay, as well as would put more emphasis on having a suppressive automatic weapon at hand.
An overheating feature would be even more important, in combination with "suppressive fire" and "weapon jamms/malfunctions" features (if implemented). Even without them, overheating could have some impact, with a degradation of accuracy from a hot barrel.