To expanded upon my Force-sensitive buddy above... really, the only think you have to worry about it data corruption/loss. At any given moment, there may be bits of pieces of data that haven't gotten written to storage, flushed fromt the cache, etc. Now, on Android, the system stuff is usually tucked away nice and safe in a read-only, static partition... so the chances of the system stuff getting corrupted in ordinary use is pretty slim. Even user data corruption is pretty rare.
Now, doing a hard-reset during a system update (which people do more than you would think), well, here be dragons.