Depends on your route. On my commute it can be counter productive to great trainign program due to the fact i cannot avoid hills. Going 5 days a week means no recovery days. If your route is flat you can use some days as active recovery rides and keep your heart rate low for the whole route. On my route, i cant keep my heartrate below certain zones without taking a bus .

Typically commute miles work as a combo of base miles and junk miles. But they are still better than car miles.