Yes, weights are very important to define relative priority of every item and to accurately calculate the roll-up values from KPIs to the Global result.
You must define them when you create or edit a dashboard. Bare in mind that the total should add up to 100% in each area. For example:
In a Financial Perspective (with a weight of 40%) I can create 2 Objectives:
- Maximize Profit (Weight: 45%)
- Manage CashFlow (Weight: 55%)
A mis-use or lack of weights would turn out in inaccurate calculations or problems in Excel Sync