it's great for applications that are notorious for requiring specific versions of libraries and can cause dependency hell. moves unnecessary system dependencies into a sandbox. for me this means i don't have to enable multilib to install Steam and pull in 32 bit libraries on my root.
while it does take a lot of disc space it doesn't duplicate dependencies in most cases. i would say you receive some good benefits at the cost of a bit more disc space, such as increased security, easy installs, explicit app permissions. it's great for when you have to install a proprietary tool in that you gain control of what it's allowed to access.