Cross chaining is absolutely common on all derailleur bicycles, simply because there can be only one proper chain line.

Cross chaining causes additional friction and, of course, wear. A bike that has been cross chained a lot, will show the wear on the alloy chain rings. The sides of the teeth will be dramatically worn. Look at the teeth on the big ring and compare to the middle ring. The middle ring still has lubricant sticking to the teeth, while the big ring shows clean/ground sides to the teeth. This is what cross chaining does to your machine...



The wear on the cogs will not be as noticeable, but will, none the less, be present. The wear on the chain will also be accelerated, causing the chain to appear to stretch more rapidly, causing tooth wear, once again, to rings and cogs alike.

So, cross chaining is not good, when seeking dependability and longevity from the bicycle and its drive componentry. Cross chaining is not good when the rider is seeking optimal performance.

Big issue or small, cross chaining is a foolish way to treat a bicycle's components, even if you can't hear all of the wear and power robbing that is taking place.