Faeries are like monkeys.
Reader's Digest had an article last year about Helping Hands, which provides highly trained monkeys for people with severe spinal cord injuries / mobility impairment. The monkeys can operate microwaves, TVs, etc. Very helpful - though they can still get into mischief! (RD's article mentioned one helping monkey who frequently stole the peanut butter and hid it in her cage to snack on later.) Helpful monkeys, but still with great potential for mischief and destruction.
Normally, however, you don't want monkeys in your home. Not even as pets; they might be sweet as babies, but then they grow up, and if they get bored, they'll get destructive. Or as adolescents or adults, they'll have sudden mood shifts and get aggressive. If a wild monkey gets into your house, that's even less fun.
Japan is being overrun by monkeys; people fed the monkeys and now the monkeys demand that food, and they'll attack for food, and so on. Stores have closed because of monkey theft. People can't leave their doors or windows open for fear of monkey invasions. Monkeys in Jorhat are a menace as well.
In other words, the occasional monkey can be friendly, helpful, and an asset in the home - with great care and effort and attention. Most of the time, though, monkeys are pests and dangerous and destructive, and you don't want them around.
Faeries are pretty much the same way, the way I see it. They can be useful, helpful guardians if treated correctly and carefully (though they'll still steal little things and cause problems here and there) and in small doses. Most of the time, though, they invade and run amok and infest and break things and mess with electronics and suddenly nothing works right, and you've lost half your smaller stuff, and the faeries run your home (badly).
So when someone opens their door and says "I welcome the faeries into this home!" and asks around on pagan boards "How do I invite the faeries into my household? They're so pretty and glittery and wonderful and amazing*!", I wince. Because oftentimes it's like opening your windows and doors and setting up shiny trinkets in the windows and food in the open in the middle of Japan or Calcutta and saying "HEY! MONKEYS! You're adorable, I want you to live in my home with me!
Such cute ikkle monkeys, come into my house, enjoy my shinies!" and then being confused and uncomprehending when the monkeys storm in, bite you, break your stuff, steal your shiny things, eat all your food, toss around your belongings, rip your curtains, and generally make an utter disaster of your house.I know some people can manage it responsibly. I know it's possible to have a good relationship with some fae, and have fae guarding your property or your person, or helping take care of your household (like brownies), but I still think it's risky. They're going to still take stuff as their due (on top of whatever you're offering them as compensation anyway), at the very least.
If you can manage to form a relationship that's more help than harm, good for you. I wouldn't risk it, myself. Faeries scare me. I'd rather just leave out some milk and honey as a peace-offering, "here, take this and leave me and mine alone," and leave it at that. Most of them are Outsiders in my opinion (to use ADF terms), not entities I want among my stuff!
((Please note that I'm not talking about fae-kin. Fae-kin aren't small and invisible and so most of the time you can keep an eye on them... and from my experience, the only things you really need to watch around fae-kin are your emotions, your sex drive, and your relationships.))
