Well, if you are on a trajectory of a 30-year career job at one company with little to no changes in your income but adjustments and raises, then you probably don't need such a community. But judging based on Boggleheads forums, there's a need. Yearly re-balancing, changing your goals, windfalls, unplanned expenses, adjusting for tax efficiency, switching jobs, re-doing your portfolio because you did it horribly when you started, helping others who have a messy portfolio, and of course, the many questions every n00b has when they start.

Of course, Boggleheads would do just fine for any of these, but more options never hurt.