Once in a while Spirit
might start to feel some kind of affinity towards a human. See some similarities between the two of them. But instead of trying to possess
them, taking over their body completely, they'll just start to follow them, stalk them, but also protect them. For the most part, a spirit that haunts someone will stay around them in their immaterial form, only showing itself once in a while, somewhere in the corner of their eye. But as the "bond" starts to grow, it'll start to show up more, sometimes trying to help in any way it can (which might not always be beneficial for a human) or just to look at their favorite human and spend some time with them.
The frightening protector
A lot of spirits don't really understand that their appearance, them suddenly showing up, or them keeping stalking someone might be terrifying to someone or even perceived as hostile behavior. Similarly, even if people might understand that the presence of the spirit might be beneficial to them, not everyone will agree to have a stalker, especially if said stalker looks gross, disturbing, or simply scary.
Getting rid of a haunting
To get rid of haunting, one needs to get rid of the spirit. Depending on its taboo or the strength of the spirit, it might be ridiculously simple or plain impossible. There are stories of people being haunted by hundreds of spirits of the same type, that all liked their host.
Some stronger spirits might survive an exorcism. Some, whether understanding what their "friend" tried to do or not, might simply show up again, stuck in a cycle of getting banished, regaining their strength, showing up to help their "friend" again, and getting banished again. Some might become hostile, either trying to take revenge on those who hurt them or trying to possess and merge with them forever, so they are never cast away again.
Positive sides of haunting
Spirits that haunt someone might try to help them in many ways. Depending on their own skills and capabilities, they might try to warn them of the danger or show them things they have found in the area. They might inspire them with their concept or do something for them.
What's most useful, the haunting spirits won't let any other spirit possess their "friend". Should any other spirit try to do so, they'll try to drive them out, and if it turns out they are too weak and their bond to their "friend" is strong enough they might try to get rid of the intruder by sacrificing themselves, either fighting to death or merging with the hostile spirit so they both become something else or fade into nothingness.