In acute stroke previous research has suggested that managing hyperglycaemia could limit neurological damage and improve outcomes. However, a recent Cochrane review suggests that there is no benefit.
"Evidence from this systematic review indicates that, compared with control intervention, the administration of insulin to maintain glucose within a specific range immediately after acute ischaemic stroke does not reduce dependency, neurological deficit or mortality at 30 days or 90 days. These findings did not change in the subgroup analysis of those with diabetes mellitus compared to those without diabetes mellitus. There was, however, a significant increase in episodes of hypoglycaemia in the treatment group. This review provides no evidence to support the use of intensive insulin therapy for tight glucose control after acute stroke." 
1. Bellolio MF, Gilmore RM, Stead LG. Insulin for glycaemic control in acute ischaemic stroke. Cochrane Database Syst Rev 2011;9:CD005346. Available from: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD005346.pub3/full