Yes but then you loose the bulk discounts. Getting 2 days (for one person) worth of veggies, meat etc isn't much cheaper than eating out. Plus the time spent doing the grocery shopping 3 times a week, with the time to cook the individual portion, then cleaning up for me just wasn't worth it. Individual preference obviously, but just didn't make sense for me most of the time.
You can definitely argue on the time aspect, it is definitely much longer, but if you actually start adding tax and tip and really look at transactions, there's no way that eating out is anywhere close than food cost.