Yes, they need you.
Yes, they need your help.
Yes, they need your experience.
But you know nothing about the project.
You know nothing about the people.
You know nothing about the history, the context or the goals of what is trying to be achieved.
You know nothing about what people have been through and what they need.
You might have been hired to do X but what people need on the project is Y.
Be flexible, be understanding, start slow, learn, present, ask questions – when you know the landscape, then deliver.
As with any new team, the biggest key to your success will be adoption of the team you are joining. Get them on board, get them seeing your ideas, get them to buy into them.
Team Adoption has the greatest of success rates in any endeavour (no need to go into the alternates because they aren’t worth it).