Yes. A removable black cover lets one umbrella work in two ways:

• cover on: use it as a reflective umbrella, aiming the flash into the umbrella so the light bounces back toward the subject
• cover off: use it as a shoot-through umbrella, aiming the flash through the translucent fabric toward the subject

That makes the umbrella more flexible than a dedicated single-purpose model.

In practice, shoot-through use lets you place the umbrella’s white surface closer to the subject, because the flash sits behind it instead of firing into it from the front. Closer light is usually softer, and the light falloff is faster. Reflective use places the lit surface farther away by roughly the umbrella shaft length, which can change both softness and falloff.

The answers also note a general character difference: shoot-through tends to be more contrasty, while reflective bounce tends to wrap the subject more. The tradeoff is convenience: convertible umbrellas are handy, but swapping the cover on and off can be less convenient than owning separate dedicated umbrellas.