AtoMaki, I'm not sure about this, but aren't only Astropaths bound?

Nope. A Bound psyker is anyone who has firm control over his psychic abilities. A rogue psyker with strong self-discipline is also a Bound psyker though he isn't Sanctioned. A Space Marine Librarian is also a Bound but he isn't Sanctioned. Most Xeno psykers (like the Eldar) are also Bound but not Sanctioned.

Sorry, but I'm pretty sure that's not the case:

http://wh40k.lexicanum.com/wiki/Soul_Binding#.UpyHuNKko3I

Sould binding is actually a rite binding the soul of a psyker to a stronger entity, giving them some measure of safety while manipulating the Warp. I already knew that Astropaths were soul bind, as it is necessary for a human mind to project itself between planets.

However, I believe that I read in some DH book that psykers can be bound to daemons and such, granting similar effects.

I am not sure about that part, however.

Sould binding is actually a rite binding the soul of a psyker to a stronger entity, giving them some measure of safety while manipulating the Warp. I already knew that Astropaths were soul bind, as it is necessary for a human mind to project itself between planets.

Soul binding is Sanctioning itself. Being a Bound psyker is not the same. Yeah, the name is confusing but even the "Class of Psykers" section differs Sanctioned and Bound psykers (it lists all Sanctioned psykers as Bound but not all Bound psykers as Sanctioned).

The term "Bound" in the case of psyker class refers to who is in charge: for Bound psykers, the psyker is in control - for Unbound psykers, the psychic power is in control. Or to better say: the psyker has either bound his psychic power (so he is a "Bound" psyker) or not (so he is "Unbound").

OH!

You're talking about Bound Psykers, not SOUL Bound Psykers!

Actually this, right?

With that said, do you think a talent for this is necessary?

It seems to me this is just a definition, not a technical term with different mechanical abilities. The technical differences are present in the "classes" presented, I would think.

OH!

You're talking about Bound Psykers, not SOUL Bound Psykers!

Actually this, right?

Bound: Sanctioned psykers and Astropaths, sorcerers, Librarians, Chaos Space Marines, and psykers from xenos species.

Yes, I was talking about them .