While it seems wasteful, discarding a portion of your starter with each feeding, it is a necessary step in establishing a healthy microbial balance of beneficial bacteria and wild yeast. In order to provide enough food for these microbes, you must stir in a slurry of flour and water to equal the weight of your existing starter. If you never discarded a portion of it, you would soon have an unmanageable volume. Discarding a portion with each feeding keeps a proper microbial balance and makes maintaining your starter easier and more manageable.