First off, I think it would be good to define the terms "eating out" and "cooking". The latter is a no-brainer since it involves you buying the ingredients, and then using the cooking instruments to create something delicious (hopefully). The former, "eating out", is more complicated as there are levels. I'll say all the levels of "eating out" share similar characteristics: traveling somewhere, spending money, obtaining an already-made food product, and...eating it. But we can differentiate the levels based on cost, waiting time, healthiness, and class status. Let's describe a few examples (in an increasing order of class status):
- McDonalds -- it's cheap, quick to receive the food, but has very little class status. Labeled as a "junk food" factory. Not very healthy overall, but a few items can surprise you.
- Chipotle -- a little more expensive than McDonalds, but it's also relatively cheap for the amount of food you receive. Arguably shorter waiting time and overall with an "okay" health factor. The food is actually good quality, but the serving sizes are enormous.
- Boutique eateries such as "Sweet Green" -- I rarely venture into these but overall, these are niche restaurants similar to Chipotle but with more unique offerings. Healthiness on these tend to be very high, like "Sweet Green".
- "Fridays" and "Red Robins" -- here we wade into the area where one has to sit-in to eat at these restaurants. They are amongst the cheapest in this segment, with average waiting times, but the healthiness is questionable. Think of them as extensions of the fast-foods like McDonalds. They can be niche, but largely serve a wide variety of products. Generally speaking, any sit-down place is regarded as higher in class than otherwise.
- "Cheesecake Factory" -- the Chipotle equivalence to McDonalds, these are restaurant chains similar to Fridays, but with higher prices and a higher class status. Food is pretty good but, again, serving sizes are enormous.
- Boutique restaurants like steak-houses -- these are almost identical to the boutique eateries described above, except with the sit-down requirement. Can be regarded as even higher in status than the above, since they are specialty places.
- The five-star restaurants -- these are amongst the highest in class status, highest in prices, and often also on waiting times. I only been to one of these in recent memory and I remember it being an expensive affair. Food was average in my opinion.
For our purposes, we will stick to the first 3 tiers that I defined. The main reason is that young professionals either can't afford frequenting at the higher tiers, lack the time, or a combination of the two. The first 3 are quick, relatively inexpensive, and easy to hang out with company.
Compared to cooking, eating out (at the first 3 tiers) is advantageous in terms of time and variety. The most significant factor might be time. In order to cook, you would have to acquire all the ingredients necessary to prepare the meal, spend time cooking, and finally eating. Buying ingredients may be very time-consuming if ingredients are difficulty to come across -- and very expensive if, say, you only need a fraction of a package. When eating out, you can just place an order and...eat. A very simple two steps (obviously I am skipping the waiting part). As mentioned, you have the flexibility to pick out whatever type of food you'd like to indulge. There are (many) foods that young professional simply cannot prepare.
The advantages of eating out being laid out, what are the disadvantages? Well, the obvious one is cost. If one averages $5 per meal (a burrito is about $7 at Chipotle vs $1 McDouble at McDonalds), then the weekly cost of eating out will range from $70 to $105 -- depending on whether breakfast will be skipped. A more sensible estimate might be $90 per week. Picky eaters may raise this tab all the way to $140 per week. This total translates to $360 to $560 per month! This would be a significant expense for most young professionals. Comparatively, cooking meals and packing lunch while occasionally eating out results in a sub-$300 food budget (my own figures).
But what people often ignore is food safety or, in other words, the sanity of restaurants and other places. In most cases, a person's kitchen is much better organized and sanitary than restaurants. Eating out thus results in an externality (economist speak for "non-calculated cost") that can be very significant. Furthermore, one has little control over portion sizes and quality of the food being prepared. Returning to a previous point about cost of ingredients, how do you know the meat patties from McDonalds were not left overnight? Or the Alaskan salmon you ordered is really Alaskan salmon? You'd have to trust the restaurant to be honest in its advertisements.
Personally, I tend to cook about 3-4 times a week. Most of the time I cook a two portion-meal every other night: 1 portion to eat immediately, and another to take to work the next day. Sometimes I make so much that I save the extras as a snack. The biggest draw to cooking is the ability to learn about cooking and come to appreciate cuisine for what it is. It's also simple and cost-effective -- a good stir-fry simply requires the ingredients, a wok, and a rice cooker to make a side of rice. The results are surprisingly good.