The polls are a snapshot on how the campaigns are doing. If they were taken a month ago that means things are even worse now. Most of the polls I've seen on CNN have been more recent than that and things are not going well for Donald Trump. The polls are an incentive for him to make changes to improve but it doesn't look like he needs that.
Polls are helpful tools to determine where people currently stand in regards to a variety of issues. Learning the opinion of the public more than a month ahead of the election allows the Clinton campaign to adjust political tactics and address the public's concern. This information may help Clinton surge even farther ahead in the poles for the battleground states.
Yes, some polls that are taken more than a month before election day are helpful. These polls do not predict the winner, however, they let the candidates know how they are doing on the key issues of the moment. It makes little sense to beleive that the way that people will vote in teh election will change much in two or three months.
Polls are not helpful in general. They simply encourage people not to vote because they think that their canidiate has no chance of winning or that thier canidate will win by a landslide so there is no reason for them to vote. Polls actually hurt the election by changing the way people vote.