Adding Expected Progress points to your goal's timeline allows you to set targets that you want to reach between specific dates. These targets may be equally divided along your timeline (every week/month/quarter), or you may expect to make more or less progress at points in your timeframe.
You might want your progress to increase equally across your timeframe, for example increasing by 25% each quarter to reach 100% by your due date.
Or, you might expect to have uneven progression or updates across your goal's timeline. For example, you might not expect any progress to be made in the first two quarters but expect about 75% made in the third quarter, and the rest by the end of your year.