Consider the difference between eating in at McDonald’s, or using the drive-through. When eating in, you have to follow certain rules, and you’re limited by what they offer. If you really like sriracha on your burger, for instance, or you want to pair fries with champagne, you’re probably out of luck. However, if you use the drive-through, you can easily take your food home and hack your meal into something truly special. Whichever way you choose to order, it’s still the same food coming out of the same kitchen. Using the drive-through, or ordering in, just gives you a bit more flexibility in how you choose to consume your food.
The same logic applies to websites. Traditionally, WordPress sites have been designed like dine-in restaurants, where the entire experience is managed inside a single location. Visitors to your website sit in the dining room, and food is delivered from a kitchen that’s just a single swinging door away. There’s nothing wrong with this approach, and for many purposes it works very well; however, it lacks flexibility. You can’t easily renovate the kitchen, for example, without people going hungry in the dining room. If you want to renovate the dining room, the kitchen will have nobody to serve food to. And if you happen to find bugs in the dining room? There’s a good chance they’re in the kitchen, too.