Well, it's not bad for your fish . Small amounts can indeed consume nitrates and provide a good snack for certain fish and inverts. I personally leave some in...usually on the rocks or driftwood. You never want to completely clean everything.
However, algae in excess can be a sign of a problem. Sometimes tanks with a lot of algae are getting too much light, too much fertilizer, are over-stocked, or don't get enough water changes. That's not always true but if you notice a lot of algae growing it's always a good idea to see if any of those issues are causing it .
i tested all my water again today, to make sure everything was still good.. ammonia nitrites and nitrates were all at zero, i'd assume thats from the spots of algae begining to grow on the back wall of the tank..?