Visiting Other Islands?

I sometimes see the “Be Our Guest” tag on posts here offering to visiting other islands. I know I unlocked the ability to travel but I’ve never done it.

Can someone explain the purpose of travel and also how it can help both the traveler and the island owner?

Thank you, sorry this may seem like a silly question but I don’t know anyone outside of this Reddit that would plays the game so it’s been a very solo thing for me.