What is the main goal of introducing signals in Angular?

The main goal is to simplify reactivity in Angular and make it "transparent" for the developer. Signals give a clear model for working with state without subscriptions, async pipes, OnPush, and unnecessary magic around Zone.js.

To put it simply, for a junior:

Signals were introduced to:

1. Manage state more simply, instead of streams and subscriptions there is an ordinary variable with a value.
2. Update the UI predictably, when a signal changes, Angular knows exactly what needs to be re-rendered.
3. Get rid of unnecessary subscriptions and memory leaks, nothing needs to be manually unsubscribed.
4. Speed up the application, only what actually changed gets rendered.

So Signals are a more convenient and visible way to do reactivity, where changes in data and changes in the template are connected automatically and without extra code.