In "Unimatrix Zero (aspect 1)", it was so the Doctor could keep track of her REM sleep and try out to ease her nightmares about Unimatrix Zero. In "Imperfection", it was to track the general performance of her malfunctioning cortical node. Given that Voyager was stranded in the Delta Quadrant as a result of Janeway's actions, whatsoever the factors behind them, this could be a circumstance of her getting "kicked upstairs.