What Wave is good at
Wave is well known for offering a generous free tier of invoicing and basic accounting features. It is focused on the US and Canadian markets, where its payments and payroll add-ons are concentrated, and where the bulk of its user base sits.
For hobbyists, side projects, and very small businesses in the markets Wave serves natively, the price (free) and the simple flow are a fair match. The product gets you to a sent invoice quickly without much ceremony.
Feature availability, payments support, and pricing vary by region; check the Wave site for what is offered in your market.