Do I need to annotate all pictures in the image?

I've started annotating using LabelImg tool and drawing boxes but I have too many pictures in the images (like lots of grapes in the image). For better trained model, is it required to box all pictures or is it okay to leave some?

I am trying to train a Faster RCNN model.

example: Thanks

I think as long as it's not getting too small bbox and, visually recognizable to the human, or possible to get features within it - that's fine.

For example let's consider the following cases, a dataset contains such meaningless annotation (red marked) which normally an engineer would skip those bounding boxes (box['w'] * box['h']) < some threshold.