Some are, some are not.
In this case, a powered subwoofer uses a "plate amplifier". If they are under 300 watts, they are worth it. Powerful powered subwoofers over 500 watts aren't worth it. Because, the plate amplifier is installed inside and onto the enclosure. When the subwoofer hits hard and loud, the subwoofer does damage to the plate amplifier.
Here is what people experience when the "plate amplifier" is damaged.
1. The amplifier does NOT turn on. (Very common)
2. The amplifier clips on and off. (Common)
3. The subwoofer NO longer hits hard and sounds good. (Common)
4. Lacking of low end frequencies. (Rare)
5. The same frequency produces out. (Very Rare)
6. The amplifier heats up, burns up, smokes up. (Very Rare)