It adds a chunky piece of plastic at eye level, to make you look dorkier while wearing the headphones. (Disclaimer: I have no ill will towards PortaPro owners, this sentiment is borne of the self-loathing I feel when I look into the mirror while wearing them). I’d really prefer it wasn’t there, I don’t find it useful, and it ruins the retro aesthetic in favour of a Borg implant cosplay aesthetic.