I see that Mitch is a former regional airline pilot just as I used to be. I've lived in a crash pad. I've breezed through Mitch's posting but thought I might hammer out some details for you to read, apologize if this duplicates anything Mitch has already said, he obviously put a lot of effort into his post.
First, I would estimate a majority of airline pilots do not live in the base they are assigned to. This means they commute to and from work.
There are many reasons a pilot doesn't live in his/her base. First, there is only a handful of airlines, each with bases in different cities. Airlines, especially smaller commuter ones, open and close bases ALL THE TIME. It doesn't make sense for a pilot to move to the base only to have it closed down a year or two later. It's tough on the spouse and kids to be moving each time an airline decides to do this.
Now having said that, certain bases are always going to be bases. IE United is not pulling out of Chicago ever, etc..
Next, airlines have more than one base. Another reason to commute to work. I might be a senior First Officer and have spent the last few years based in Denver, but if I upgrade to Captain, I'm going to be a junior captain and my seniority might not allow me to stay in Denver, I may be forced to be based in Chicago instead. You get the idea.
Now, there is a huge difference in pay between a Regional Airline new First Officer who only makes $18,000/year and a senior Captain at United in his last few years before retirement making $200,000 plus per year (and always decreasing, not like the good old days).
The junior FO making $18,000 will have no choice but to rent a crash pad if he doesn't live in his base city. He'll be on reserve which can mean a lot of sitting around at the base with no overnight trips paid for by the company.
So he needs a crashpad.
The crash pad I lived at had about 20 people living there each paying $100 per month. It was a 5 bedroom house with 3 bathrooms. 2-3 cots per room. Here's the thing, not all 20 people are ever there at once. The most I had ever seen in the house at one time was 8 people.
Anyways, if you can make the math work, its doable, but someone has to be responsible for the place.
Now, for the more senior captain, he's probably in the domicile he wants and is never leaving until he retires. Maybe since this will be his last base, he'll actually move to this city and stay there. In this case he doesn't need a crashpad.
But, on the other hand, he may not be willing to give up that Southern California lifestyle and will need a crashpad, but he makes more money so he's going to be in something a little more "refined". Maybe him and 3 other pilots buy or rent a 4 bedroom house. Nobody but those 4 people will ever be there and they each pay there share of rent or ownership.
So that's how it works, it's a crazy lifestyle and I was an airline pilot for 6 years, but I simply had enough. It's not as glamorous as it used to be. Certainly doesn't pay anything anymore and we've lost our pensions.