Both lobectomy and segmental resection are surgical treatment options for primary lung cancer. The main reason why segmental lung resection is chosen is that it is beneficial in protecting lung function, how exactly? One study included 184 patients who underwent segmental lung resection as well as 208 patients who underwent lobectomy between 2013-2016. A matched analysis found that segmental lung resection significantly preserved more total lung function compared to lobectomy (p<0.001). Lung segmental resection preserved 48%±21% of the preoperative lung function of the operated lobes. Lung function in the ipsilateral unoperated lobe was significantly higher after segmental lung resection (P=0.003). In contrast, there was no improvement in lung function in the ipsilateral unoperated lobe after lobectomy (P=0.97). Contralateral lung function was significantly improved after either lobectomy or segmentectomy (P<0.001). This study found that segmental resection had a significant advantage in preserving lung function over lobectomy for the following main reasons: (1) segmental resection was able to preserve lung function in approximately 50% of the operated lobes; and (2) lung function of the ipsilateral unoperated lobe was significantly improved after segmental resection but not after lobectomy. As for why the lung function of the unoperated lobes was significantly improved only after segmental resection, it may be that (1) due to the large tumor resected in the lobectomy, it is possible that the lung function of the located lobe was impaired preoperatively, which in turn has caused the compensatory growth of the other lobes of the ipsilateral lungs preoperatively, and thus there is no room for improvement of the lung function of these ipsilateral unoperated lobes postoperatively; and (2) after lobectomy, it is possible that it has caused the ipsilateral changes in the anatomical position of the unoperated lobes, thus hindering the improvement of lung function. In conclusion, these study data suggest that compared with lobectomy, segmental resection is effective in preserving total lung function. The reason for this is that lung segmental resection not only preserves the lung function of the operated lobes, but also enhances the lung function of the ipsilateral unoperated lobes. Lung function of the ipsilateral unoperated lobe cannot be enhanced after lobectomy. Contralateral lung function is enhanced regardless of whether the lobectomy or segmental resection is performed. Localized postoperative lung function enhancement may arise from compensatory lung growth.