More people might buy the product with feature X. Should you build feature X?
Not necessarily. A startup’s cash-on-hand is shrinking every day. You want to add the features that will do the most to stop your losses. You don’t execute every random idea without prioritizing it.
Not just a startup. ANY business. Weighing ideas and prioritizing them is the hardest work you'll do.
Steve Jobs does customer development: No new features - Venture Hacks