Obviously this varies, but if you have a good relationship with your manager, this can be a huge benefit down the line. That person can be part of your professional network, and may possibly reach out to you several years down the line with a new position at the new company they work for. Leaving right after a large project has been assigned to you does have a negative impact on your manager and current team, so it may be beneficial to let them know early.

People change positions fast in this industry, so keeping on good terms with coworkers you respect can be good later when they have moved on and are looking to hire.