I cannot overemphasise the importance for early-stage companies to create an Advisory Board.
The founder and management team, more often than not, are very closely involved in the business on a day-to-day basis. As such, they can do with inputs from an Advisory Board which meets once a quarter or so to review the business and give critical feedback on the future plans. The semi-detached view can help in opening up new lines of thinking which the management team sometimes misses because of their proximity to the daily operations.
What is needed for this relationship to succeed is complete candour on both sides. If it can be made to work, the Advisory Board can be a tremendous advantage for the start-up.