I haven't seen this mentioned yet (or maybe I missed it) but it appears the Time Machine can actually kill a nearby sim.
An elderly neighbor stopped by when my sim was using the Time Machine, and she was standing right next to it. All of a sudden, the neighbor started sparkling and turned into a ghost, and I got a message saying some stuff about how my sim had tried to warn the neighbor about the radiation from the Time Machine but a time guardian had prevented him, and then grim reaper came and took the neighbor.
Sure came as a surprise to me. The neighbor was already old, but considering a message popped up it doesn't seem like it was a natural death. Can the Time Machine accelerate the aging of younger sims nearby?