The main role of nasogastric decompression in sub-acute intestinal obstruction is to relieve proximal distension by removing accumulated gastric and intestinal secretions. This reduces intraluminal pressure, prevents bowel wall ischemia, and decreases the risk of perforation. It also helps to control nausea and vomiting by decompressing the stomach. Nasogastric tube placement does not directly prevent infection or promote healing, nor does it reduce fever. Its primary purpose is mechanical relief of pressure to stabilize the patient before further intervention.

Reference: Sabiston Textbook of Surgery, 21st Edition.