One of these at the top of your rack, and another at the bottom, will help set up a little convection current of air running over the hot gear in the middle. Think of them as the venting panel bread in a hot gear sandwich. Since keeping your rack equipment cool prolongs its life and ensures its day-to-day reliability, and since fans and extractors are noisy, these little panels are very worthwhile.
Be aware that because most of the length of the panel is punched through with apertures, these aren't as sturdy as solid blanking panels; they bend more easily, and sometime have arrived a little warped. That said, it's a moment's work to gently bend them back; and once installed they look very neat and professional.
