In Angular, forms are an essential part of any application as they allow users to interact with the application and provide valuable data. Angular provides two approaches for building forms: template-driven forms and reactive forms. Both approaches have their own advantages and disadvantages, and the choice between them depends on the complexity of the form and the requirements of the project.

Template-driven forms use directives, such as ngModel, ngForm, and ngSubmit, to bind the form controls to the component's properties and handle form submissions. They are easy to set up and are suitable for simple forms. For example, creating a simple login form can be achieved in a few lines of code:

 <form #myForm="ngForm" (ngSubmit)="onSubmit()">
  <input type="text" [(ngModel)]="username" name="username" required>
  <input type="password" [(ngModel)]="password" name="password" required>
  <button type="submit" [disabled]="myForm.invalid">Login</button>
</form>

On the other hand, reactive forms use a more programmatic way of building forms, using the FormControl, FormGroup, and FormArray classes from the @angular/forms module. Reactive forms are more flexible and powerful, and are suitable for complex forms. They allow for fine-grained control of the form's behaviour and are easily testable.

Reactive forms also allow for easy validation and handling of form errors. Instead of using directives to bind the form controls, you can create a FormGroup and add FormControl instances to it. You can then use the FormGroup instance to handle form submissions, set and update form values, and validate the form.

import { FormGroup, FormControl, Validators } from '@angular/forms';

this.form = new FormGroup({
  username: new FormControl('', Validators.required),
  password: new FormControl('', Validators.required)
});

Another advantage of reactive forms is that it allows you to handle form changes with Observables. You can subscribe to the valueChanges or statusChanges observable to be notified of form changes and take appropriate actions.

In conclusion, both template-driven and reactive forms have their own strengths and weaknesses. While template-driven forms are easy to set up, and are suitable for simple forms, reactive forms provide more flexibility and are suitable for complex forms. Ultimately, the choice between the two approaches depends on the requirements of the project and the developer's preference. It's also worth noting that it's possible to use a mix of both approaches in the same project, depending on the specific needs of each form.