Is it necessary to unsubscribe from observables created by Http methods?

Do you need to unsubscribe from Angular 2 http calls to prevent memory leak?

 fetchFilm(index) {
        var sub = this._http.get(`http://example.com`)
            .map(result => result.json())
            .map(json => {
                dispatch(this.receiveFilm(json));
            })
            .subscribe(e=>sub.unsubscribe());
            ...