The key aim of a vagotomy for peptic ulceration is to reduce parietal cell acid output. Apart from targeting the cells themselves, the easiest way of doing this without disturbing parietal cell function distal to the site is to cut only the closest branches of the nerve. This is done with a highly selective vagotomy.
The advantage is that antral motility remains the same - there is only minimal alteration in gastric emptying. Hence, there is a lesser incidence of complications such as dumping syndrome and diarrhoea, and also a drainage procedure is unnecessary.