Sir Ian Blair's resignation in 2008 was helpful to Londoners as a series of missteps. Blair's most notable gaffe was during an anti-terror operation in 2005 in which a Brazilian man was shot dead when he was mistaken for a suicide bomber. Blair's job as the head of the Metropolitan Police wasn't backed by the mayor and he stepped aside peacefully.
Sir Ian Blair's resignation in 2008 saved Londoners further embarrassment after several disputes with then-Mayor Boris Johnson. He received no-confidence votes from the London Assembly after his department was found to be incompetent on several levels. Despite only serving as commissioner for three years, taxpayers are still footing the bill for Blair's large annual pension.
It is very easy to see, in hind sight, how to deal with a situation, so this question is fairly easy to answer. Sir Ian Blair had a, somewhat, minor disagreement with the mayor of London Boris Johnson, and he subsequently resigned as head of the police force in 2008.
No, it would not be widely beneficial if Sir Ian Blair resigned from his post, because he does an excellent job. There will always be the problem of crime in England. It is unfair to blame England's problems on one person, when that person is the one who is trying to combat the problem. He has done a sufficient job leading England's police force.
It wouldn't be that beneficial in the larger scope of things if Sir Ian Blair resigned from his post. In reality, he's doing a fine albeit slightly controversial job in said post. He should remain where he is and his performance should be reviewed from time to time. For now, he's all right.