BotBoxer helps practice the right technique in order to avoid hyperextension. When you're used to hitting something that doesn't move — like a regular punching bag — your punching technique is not ready to deal with missing. When you never miss, it creates wrong patterns and makes it infinitely hard to maintain the right position of your arm and elbow at the end of a punch.
Generally speaking, locking out your elbow should be avoided at all times: it must not straighten up completely, as this is a way to injuries and less powerful punches.
BotBoxer creates an experience very similar to a real fight: you keep missing the bag, so you're learning to tense all the muscles at the end of a punch, and a proper technique will lead to less injuries during any boxing training: whether with BotBoxer or a real partner.