Short answer: It works for both. I also recommend it for the PC if you don't care about insulation efficiency.
Long answer: This sound insulation is better suited for walls, for example to reduce the echo of a voice when recording with a microphone. It also insulates relatively well in the PC, but flat sound insulation is better for this. Pay attention to the adhesive side. The adhesive is relatively "sticky haha" and will leave a mess on the surface!