I say as long as you are moving your body that's great! For me I would prefer to do it all at once. From what I understand the longer you can go at a brisk pace the better as more stored body fat gets burned off. Not to say that walking 1 mile isn't effective, but I found once I bumped up the miles per session more weight dropped off at a quicker pace compared to when I broke up my walks. My diet remained the same.
However if you can get in 1 mile in the morning and 1 mile in the evenings go for it