I've found it useful when my 3DC defence needs to hold opponent's 3ST attack. Where is difference when turned on/off? Well, difference is in the number of shoots; successful OT defence keeps low number of oppo's shoots towards your goal. Of course, OT won't protect your goal itself, you need good DC's which are in form (7+). Also you should notice lower number of comments about opponent's chances in front of your goal (although comments aren't always relevant)
Ex top eleven player
Have players with 5* and my 2 mid fileders with 6* and ml/aml with 6*