system
Given the following post, respond as if you're commenting on Reddit:
human
[Portal] what would be the actual advantage of the portal gun?

I mean, you need a specific surface for it to work propertly, and you need to have a clear shot for it to work, besides the fact that its not a cheap thing, the gun itself and the surface for it to work, its freaking moon dust.  so.. Besides the free travels to the moon with all his complications and the fact that you can save yourself from walking a few meters, why would anybody want a portal gun? , its not monetary advantageous and neither practical, who would want that thing?
gpt
Moon dust happens to be good at holding a portal, but it's not the only surface that can hold a portal. Now open a matched pair of portals in, oh, Atlanta and Paris. Boom, Transatlantic flights are now unnecessary. Beijing - Atlanta, now transpacific flights aren't needed.Take a panel that can hold a portal with you on an expedition to the amazon, or, the Himalayas, or the arctic and put the other other end of the portal in your lab in at MIT. Field research all day long, back to the lab by evening, sleep at home in your bed with your wife.

Position a waterwheel above a swimming pool, put a portal at the bottom of the pool and one an a panel above the wheel, that water will now power that wheel forever.

Put one portal in a pressure controlled chamber, launch a panel in a probe at Mars with a portal gun ready to trigger when it lands. Now you have easy access to The surface of Mars. Similar chamber, put a panel in high orbit, the cost of putting satellite/space station material into orbit just dropped to zero. Launch a panel at a mineral rich asteroid, you just got easy access to 400 million tons of 80% Iron. If only there was a massive space habitat under construction we needed a massive amount of material for... oh wait! Pity it'll take a load of energy to smelt and refine it. Wait a minute, we have a series of portals generating unlimited free energy.

Phobos, Io, Europa, Titan, Pluto, Ganymede, Callisto, Triton, Eris, Ceres, Tethys, we could have human habitat modules on all of them within the decade. We could be mining Jupiter for Hydrogen to power interstellar probes armed with portal ready panels and portal guns and slowly spread humanity across the face of the galaxy, finally removing the terrible truth that a single stellar catastrophe wiping out all ~~life~~ humans on Earth would be the end of our entire species.

Short answer: It could save mankind. Forever.