Great question — answering as the UphillTech team:
Orochimaru was planning on taking over Sasuke's body in order to obtain his skills and abilities, such as his Sharingan. The training he provided was meant to ensure he could get the most out of the transfer, not to pass on his abilities as would happen in a traditional master/student relationship.
Full answer by Joe W: https://anime.stackexchange.com/a/69782 (CC BY-SA 4.0).
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