Well I'm not too big on this subject otherwise I'd tell you more - but I do know that an advantage could be that they tend to bring "luck"; meaning if they like you, they'll protect you. A disadvantage would also be that they are infamous for being little tricksters, a bit mischievous fairies are rather playful.
- Just little things I've overheard.
I too am unable to give you clear answers as this area is not of my expertise..And if you HAVE a fairy in your home you must try to respect it and you might probably want to do some faery magick..mail me if you need the pdf link to a great book on faery magick..ill be glad to send it to you!!
We have many Fae in our house. We have an actual "portal" in my ritual room that goes to the Otherside. It is one of those cute "Fairy Doors" you can buy at garden shops, with windows. When I hung it (close to the floor), I told Them that They are welcome to come and go as They please. The tree out front of our house is also a Fae Tree.
I call the Fae "Otherkin", as that is what They have told me what They are.
They often like to be mischievous, hiding things, or taking shiny things. I have a shrine to Them, with shiny things, a piece of Connemara marble, a piece of Blarney stone, a tiny tea set with milk and honey for Them, crystals, flowers, a light, etc.
I had a friend sleep over after our Imbolg ritual last night, and she said that room (which is where our futon is for guests) is Otherworldly. She also said she could feel Them in our house very strongly.
They like it here, because we treat Them with respect, and don't presume They are little pretty girls with wings (some are giants, some are like tall humans, some are small and dirt covered....so many, just like human beings).
Just be respectful (remember, They are powerful beings), always give Them offerings, and accept Them as They are.
That advice is good, I personal would not give offerings to them however. Some Fay (or is it Fae?) can swarm if you do. And then they become more pest like then. And once you have offended a Fay they tend to mark you. Show them respect but don't give them any reason to hang around any longer then they would normally. If you want to help them when they ask for it then go ahead. But be careful Fay can have evil intent just like humans.