Regularly chewing on only one side is often a habit, or something done without realising. It may have started because chewing on one side was temporarily impossible – for example, because of a sore on the gum, or an extracted or painful tooth. If this habit goes on long enough, the consequences become obvious: wear of the teeth on the chewing side, the lower jaw sliding towards that same side and the centre line of the lower teeth shifting, possible overloading of the jaw joint (TMJ) and pain, and facial asymmetry because the facial muscles on the two sides have developed differently. When there is no objective reason to chew on one side, this harmful habit needs to be broken.
This answer is for general information. Your own case needs an examination by an orthodontist.