I am pleasantly surprised that Google Drive has increased her free storage from 5GB to 15GB. Maybe it is due to competition – Other cloud storage providers are offering bigger storage than 5GB. I personally won’t leave Google Drive even she did not increase the capacity.
So, no need to delete files when your storage is getting near to 5GB, but it is still a good practice to keep useless files cleaned all the time, no matter how big storage you have.