What's the purpose of Guild Cards?

What's the purpose of Guild Cards in Monster Hunter World? I mean there is the achievement that's tied to it but other then that is it just a Palico and armor fashion show? I mean when I get one in game it doesn't seem to do anything. I'm assuming that I'm just not aware of the real use of them.

Solution 1:

The Guild Cards allow you to use other players Palicos for the Tailrider Safari's. They are also useful when you see other Palicos in game they will help you out.

Solution 2:

Guild Cards have a few features tied to them.

1. Ability to view the fellow Hunter in more detail
2. Ability to see the hunter's palico out on hunts and have them hunt with you as a Tailrider
3. Ability to add that Hunter's Palico to your Tailrider Safari groups
4. Hunting with someone you have exchanged Guild Cards with grants Unity, when You have enough Unity... you are given rewards (vouchers, tickets for crafting/melding, etc)
5. Show off your own accomplishments. Many customization options of the Guild Card expand with your progress (complete this quest to get a new background, for example)

It's wise to always share your Guild Card out, and accept everyone's as well (though there is a cap, reaching it is no easy task)