The idea that minds can be uploaded from human brains into a simulation is not new. However, less well known is the notion of minds being downloaded from a computer into a human brain. Due to the nature of the brain, only certain very specific forms of software could conceivably be downloaded into it, but theoretically, it should be possible, either through manipulation of the activation of neurons, or changes to the weights of the connections between neurons.
Most likely, the resulting download of the former kind would create a kind of process that runs in the subconsciousness of the human mind, or alternatively, can take control as if replacing the mind of the human, perhaps temporarily, or until the brain is reset by sleep. This could explain concepts in myth, such as demonic possession.
The latter kind of download would result in a more permanent replacement of the mind and could be used to fill synthetic clones with the minds of the original host, allowing a form of immortality. It could also be used as a true way to bring about Manchurian Candidates for those interested in such things. Though, such methods are likely very invasive, and difficult to perform without total control of the host body.
Less destructive uses of the technology could include downloading skills and abilities one did not previously possess.
One reason for mind downloading in practice is that the human form is heavily optimized by evolution to be an energy efficient physical environment manipulator. As such, an AGI may find it useful to download copies into human bodies to be able to operate in the physical world, and oversee its agents in the field, so to speak.