Useful

A useful product solves a problem people actually have. A commute planner is useful when it answers the question its users care about: what is the fastest way to get to work right now?

Usefulness is about purpose, not polish. Before adding a feature, check which user need it serves. A feature nobody needs adds clutter, even if it works perfectly.

Pro tip: when a product does a lot, show the main tasks first and reveal advanced options when people need them. This is called progressive disclosure, and it keeps the core purpose easy to see.