Is it possible to use an observable without subscribing?

Consulting articles and documentation, I saw that it is not possible to use an observable without subscribe, I have the following code in my service, why am I able to use the observable without subscribe? Wasn't it supposed to give an error?

import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { User } from '../models/user';

const httpOptions = {


headers: new HttpHeaders({'content-Type': 'application/json'})
}

@Injectable({
providedIn: 'root'
})
export class UserService {

BASE_URL: string = 'http://localhost:3000/';


constructor(private segurancaHttp: HttpClient) { }


getUsers(): Observable<User[]>{
return this.segurancaHttp.get<User[]>(this.BASE_URL + 'users')
}

addUser(user:any): Observable<User>{
return this.segurancaHttp.post<User>(this.BASE_URL + 'users', user, httpOptions)
}


I'm studying observables and this is giving me a lot of doubts.

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