I mostly come to prefer composition, this approach apparently even has a wiki page. But that's in part because I use Rust that forbids inheritance, and don't have such bullshit (from delegation wiki page):

class A {
    void foo() {
        // "this" also known under the names "current", "me" and "self" in other languages
        this.bar();
    }

    void bar() {
        print("a.bar");
    }
}

class B {
    private delegate A a; // delegation link

    public B(A a) {
        this.a = a;
    }

    void foo() {
        a.foo(); // call foo() on the a-instance
    }

    void bar() {
        print("b.bar");
    }
}

a = new A();
b = new B(a); // establish delegation between two objects

Calling b.foo() will result in b.bar being printed, since this refers to the original receiver object, b, within the context of a. The resulting ambiguity of this is referred to as object schizophrenia

Translating the implicit this into an explicit parameter, the call (in B, with a a delegate) a.foo() translates to A.foo(b), using the type of a for method resolution, but the delegating object b for the this argument.

Why would one substitute b as this when called from b.a is beyond me, seriously.