Like any exercise, writing daily helps you become a faster, stronger, more flexible and fit writer. That's what we all want right? The writing equivalent of a six-pack? There's no magic pill that replaces exercise nor one that will make you a better writer.
Daily writing must not be a sloppy endeavor. Weightlifting with bad form will not maximize your time or tax those muscles. Same for writing. A sloppy blog or journal filled with bad transitions and poor subject/verb agreement could actually hurt you by allowing you to develop bad habits.
Think of your self-editing, as one more rep. Oooh, feel the burn.