Creepy Hollows is a questionable place, but binding spirits is a very real practice.
As for whether it is slavery, it depends on the type of binding, the extent of the binding, and the nature of the spirit. There are spirits out there with very limited sentience, and some that are non-sapient.
While it is indeed possible to do something as sordid as take a dead old man's soul, bind it, and practically make him into a slave, it is also possible to take an abstract un-personified force, like a pattern, and create a talisman, with its energy imbued which acts as a gateway to that energy. This is less ''binding'' and more of a linking.
Now in between those two, you'll find a whole range of binding magics. Some are non-sapient and wild entities, much like animals, being bound in the same way that we keep pets, because the alternative is being destroyed by them. Some are egregores, wild thoughtforms with as much ''personhood'' as weak AI, and some may be very very harmful to humans, and a simple banishing would not do the job.
Suffice to say if you can bind humans, you can bind spirits. If you can enslave humans, you can enslave spirits.
As for the questions IrisMoon put forth:
1. The item is a vessel of manifestation, the binding lies behind the physical effigy it is bound to, and it's the spiritual bondage that forces obedience and constraint.
2. Depends on the spirit. Most entities don't need to be bound to help you, and in my experiences, a friendly and free relationship is best. The main reason I oppose things like the Lesser Key of Solomon is because of that. If the item is nothing more than a link to the spirit's energy, or current, then you have your answer there, it's an aid for the magician to connect to it.
3. If it is just a linking type of thing, almost every spirit would agree to do that, to have another vessel and gateway of manifestation here. If it is a forceful, slavery-type binding, however, I don't think any entities with sentience would agree to that. Thus, the binding is forceful. Depending on your ethics that may or may not be something you're comfortable with. Others, aren't even sentient. Some are much like computers, having limited consciousness and doing the thing they're programmed to do.
4.Not really. Everyone can use magic to get ahead in life, yet most people don't seem to be actively and consciously using it, though they are nonetheless applying it indirectly. There is also the fact that we are not exactly living in a pro-magic world nowadays.