There's a lot of benefit to the run-walk method and many of the top marathon coaches including Jeff Galloway are fans. The very biggest being the recovery time you get in the walk breaks.
Our TNT program encourages new runners to start with run-walk as it lets you really determine what level of endurance you can sustain. You can adjust your run-walk ratio as your endurance increases. There's no need to move to full-time running unless you feel up to it and want to.
I've never been a run-walker, myself, but may need to revisit this method after today.