Updated Home Office policy on reviewing cases when appeals are lodged:
UK Visas and Immigration guidance for how it considers the grounds for appeal and supporting documents of an application.
Call me a cynic, but I have never ever seen any evidence that ECOs or the Home Office seriously reconsider a decision when an appeal is lodged. A very polite request for reconsideration can sometimes get results if strong, but just lodging the appeal never seems to lead to reconsideration. If anyone has experience to the contrary, do leave a comment.
UPDATE: Interestingly, a few people have been in touch to say they have found some decisions getting overturned when appeals are lodged.
Source: Appeal review: APL07 – GOV.UK