OK so I walk when I have to, but today I ran 5 miles and no walking.  It has been almost 2 months and its unbelievable that I couldn’t run 1/2 a mile back then. I’m not breaking any land speed records, but for someone who hasn’t run in years, I feel like its an accomplishment. As you continue to train, there will be days that you do walk. I find that sometimes my stride gets off somehow and walking can help me break out of whatever weird lean/strain I have going on and focus on my form again.
I really think that form is something I don’t focus on enough. As a new runner, going and breathing can be all I can keep up with in my head. Once in a while it can be good to slow things way down and focus on getting some balance in your stride. It is still a morale booster to be able to continuously run for a full 5 miles. So if nothing else, try to get something out of your run. I don’t know if there really is such a thing as a junk mile, but I think you can work on something if you are out there running.