Paragraphs were invented for a reason. Makes for easier reading.Cabinet manufacturers need to accommodate a variety of different size kitchens and configurations. They build a slew of different size boxes that can be joined together, sometimes with fillers, that can match almost any size or configuration easily. Custom cabinetmakers build cabinets specifically for the space and configuration. Although custom cabinets may be a group of separate pieces, they are typically joined together seamlessly, so you wouldn't know the run of cabinets are not a single unit. Some cabinet builders just build separate boxes and join them like larger cabinet manufacturers. Visually, you can easily see the differences between true custom cabinets and those that aren't. It's not only the joints you see where cabinets are butted to one another, it's also the sizes of doors and the balance in accommodating the space. Non custom cabinets can be a hodge podge of different size boxes. You may have two 30", one 18" and one 27" each with doors or drawers for those sizes, upper wall units may not be aligned with lower base units. A custom job would be mathematically balanced so all the doors on a run may be equal. Other hallmarks of custom work typically include things like better quality hardware and materials as well as attention to details like carefully matching grain, color and wood characteristics. Construction methods, choices in joinery on custom work can be quite different than mass produced work. There are exceptions and times when there are special circumstances. A custom cabinetmaker can pick out a non custom job in a second. The average consumer and many so called cabinetmakers are not aware of these fine differences any may not care. Custom jobs usually cost a great deal more than "off the shelf" jobs, just like custom made shoes cost much more and take longer than mass produced ones. The majority of homes do not have custom cabinets but they are very common in commercial work. One type isn't necessarily "better" than another as far as basic function but the other factors can make a huge difference in appearance and longevity.