You're starting all three promises, then waiting for the first one to finish, then waiting for the next one, then waiting for the last one. But because they were all started at the same time, they'll be run in parallel.

Whereas if you started one promise, waited for it to finish, then started the next and so on, it would take the three seconds as they won't be run in parallel.

The code you've written can be seen as a "poor-man's" Promise.all, in the sense that it's doing roughly the same thing but less clearly. It also behaves slightly differently in terms of rejections: if the final promise in the Promise.all version rejects immediately, then the whole promise will fail immediately. However, in your version, if the final promise rejects, that rejection won't be evaluated by the await (and therefore thrown) until all the other tasks have completed.

For reasons of clarity and correctness, therefore, it's usually better to just use Promise.all rather than awaiting a list of already-started promises in sequence.