Practical vs. Project
If you don't know how to sort through all of the listings and Web sites for the mom and pop shops across town, it may be a heavy investment of time to find a part through a junkyard. Chances are professional mechanics know which yards to call depending on the part you need, but that is usually the kind of tribal knowledge they've built up over years of doing business.
Starting with blind calls to dozens of junkyards probably wouldn't be worth your time unless you live in a two-yard-town. One time-saver is to find businesses with inventory systems that track what they have at any given time. Most large salvage dealers will have data on incoming vehicles, but smaller dealers might need to physically check their stock or require you to come and check for the part yourself.
Shopping online can also save you time if you want to browse nationwide dealers because many of them network with other dealers to increase the collective junk pool of resources. And large and mid-size regions usually have the best of both options.
Even if you don't need to travel to an actual junkyard to pull the part you need from lot 172, row 345, for example, often it just takes longer to find what you need. Even with the costs savings of salvaged parts, you may still head to your big-box auto retailer out of sheer convenience. But if you need parts for a car restoration project, for instance, you might head to the junkyard for the pure enjoyment and money savings.