Work rates should be chosen according to your formation and team.
For example, you shouldn’t use a striker with a high defensive work rate if he plays alone in the front. However, you can do it using a formation with two strikers. In the same way, using players with a high defensive work rate is almost useless if they don’t feature decent defensive attributes. It’s also easy to understand that a counter-attacking style will require wingers and forwards with low defensive work rates because you will need them in their natural positions as fast as possible. Finally, you should also know that playing with two center-backs with low defending work rates is unacceptable, but it’s okay to have just one.