A Job Half Done
Before I imply my own sainthood, let me preface this by saying, I don't wash the dishes every night. But when I do, I make sure to wash all the dishes. Not just the easy ones, but even the pan with baked on cheese and spaghetti sauce. The one that may necessitate a chiropractor the next day.
I'm sure my wife would appreciate even some of the dishes washed if not all, but there's a different level of gratitude when the job is done completely and to a high standard. The same is true in the workplace.
If you offer to "cover" for a coworker, or choose to ease their workload and own some tasks, be sure to do it well. A job half done or done poorly will cause more harm than good. And will dissuade your teammates from trusting you in the future.