It is better, of course, if only garkeine vibrations are transmitted to the housing (HDD suspension, fan, ...) and a noisy fan (due to high speed, etc.) you get with these mats course not quiet - but this is not the insulation mats lies.
Tip: even smaller areas between the webs, folding etc. possible area filling paste. Any housing openings should of course not be pasted (heat or air flow!).