For me, todo lists remove the mental burden of keeping track of what I need to do in my head, and allow me to easilly shelf a new task without significant interuption to my workflow on the current task. Becuase I am at a computer for almost all of my work, my todo app is just vim, but I don't see why I wouldn't get the same benifit from a proper 'app' if I was at a job without consant access to a computer.