Yes, it's good to have an aperture ring on a lens if you're adapting it from a different mount system and it has no way to talk to the camera--that way you still have a way to control the aperture.
For example, if you use an F-mount adapter ring to put a
G-mount Nikon lens onto your Canon camera, the lens will physically mount, and you can shoot through it, but you can't control the aperture, since there's no aperture ring. With an F-mount lens, you can use the aperture ring.
I use adapter rings for Olympus OM and Contax lenses (and have used an adapter for a Nikon F-mount lens), and I have a cheap Russian (Hartblei) tilt-shift lens that all have aperture rings, and absolutely no communication with the body. I can shoot in M or Av modes only and must manually focus, because the camera can control the iso and shutter speed, but not the focus or the aperture of the lens.
The reason I use those lenses is because my Olympus OM is a 50mm f/1.2 I found for less than $300. The Contax lenses have Zeiss glass (again for <$300). And the tilt-shift was $400. To get similar glass in an EOS mount, each of those lenses would be well over $1k. I also shot in the days of film when you had to twirl the aperture ring and the focus ring for every shot, anyway, so it's not a big deal to me.
With the Canon EOS mount, you can adapt multiple mounts with adapter rings that don't have glass elements: Pentax K, Leica R, M42, Nikon F, Nikon G (special adapters required for the aperture ring problem), Contax-Yashica, and Olympus OM are all usable on EOS cameras. Just not Canon FD
.