I would not be surprised if many younger car enthusiasts have never been to a wrecking yard. Especially if they are not a "hands on" kind of guy. If you are mostly involved with later model cars then parts are still readily available at your local auto parts store. For older cars sometimes the only readily available parts are used, either from an online listing. a swap meet, or a wrecking yard. Many refer to this venue as a junk yard, which is really a misnomer as that yard is full of gold, not junk.
These can be tragic places for the enthusiast. Once gleaming objects of desire are reduced to smashed, dirty, smelly cadavers. Even the mighty will have fallen. I saw a late 90's Jaguar supercharged V8 XJR sitting at a local Pick and Pull. The body and interior were in fine shape, The motor area looked undisturbed. My guess was that either the cam chain tensioners gave out or the car blew a head gasket. Either way the cost of the repair exceeded the vehicle's value. I've seen lots of cars like this offered on Craig's List. The seller coyly referring to it as a "mechanics special" No lie. No takers either. So it found it's way to the scrap heap. Still it might provide some one a perfectly serviceable supercharger. Or brake system. Or cool mesh grille. So much good can be found picking over the bones of the dead.
There are many types of good parts available, especially body parts, trim pieces, and interior components. Mechanical parts such as steering and suspension, radiators, manifolds, and brake parts. Consumables, like brake pads, suspension bushings, spark plugs, belts and hoses are better bought new. Starters, alternators, power steering pumps, rack and pinions can be a good deal if you thoroughly check them out beforehand and you are aware how much a new or rebuilt part will cost. If there isn't a substantial savings then go for the new part.
The overall appearance of the donor car can tell you a lot. A clean lower mileage car that was junked as the result of a massive rear end collision can yield an engine bay and front end full of good parts. Relatively current oil change stickers indicate that this car was recently driven until the fortunate event. Look in the glove box for any receipts. Cars with a heavy, stubborn looking coat of dirt, worn out interiors full of trash, and faded paint with rusty panels usually have sat abandoned and unmoved for many years. It seems that the only 50s and 60s cars I find nowadays in the yards are in this condition. A very heavily rusted car may have sustained major fire damage. I don't have to tell you to avoid these cars. Sometimes though, you will luck out.
Once, when I was looking for engine parts for my '66 Riviera (cylinder heads in this case) I found a car with a very clean looking motor. I looked under the rocker arm covers and saw that the motor was free of sludge. I pulled a couple of plugs and they were nice and clean. As I was inspecting the underside I saw a small plate attached to the block that carried the name of an engine rebuilding company. I had noticed the the inner wheel wells had been painted white and the car had sustained major rear end collision damage. I interpreted this to mean that some one had been fixing up the car by having the engine rebuilt, added some nice wheels (hence the white wheel wells) but the car had been wrecked and was not worth the cost of repair. I bought the motor and installed it as found in my Riv. The motor ran great and gave me several years of good service. Now that was a real bargain.
Back in the day there was only the full service yard. You walked up to the counter and told the man what part you needed. He then called out over the intercom to the yard man to go pull the part off and bring it upfront. The customer was limited to the area at the front of the establishment. There was usually a display of shiny hubcaps, some tail lamp assemblies, a nice clean front seat and maybe a set of factory mags or rally wheels. Off to the side might be a smaller room with a display of used tires, or even better, a rack of used motors, with their mileage written on the valve cover with that thick yellow paint pen. All with a 90 day guarantee! I remember going with my Dad to those wrecking yards when I was a little kid. They seemed to be filled with so much potentially cool and useful stuff. If I could only get in and take a look! And there was that wonderful distinctive smell, of old caked on dirt and grease. That can trigger some real nostalgia. For some reason modern yards just don't smell the same.
Modern self service lots allow you to go in, wander around and help yourself. I'll walk around looking in different cars, especially the fancy ones and imagine what I could use and adapt. A lot of patrons don't use a lot of finesse removing parts. They will pretty much tear up and break surrounding components. It always strikes me a somewhat disrespectful.