The closet door requires specific knobs even before considering the intricacies of changing locks. Perhaps the place where this is best demonstrated is the hallway or any other enclosed space on the property. There are two major approaches to doing closet doors. The first is the ball catch closure. Here the closet has a ball which is loaded using a spring. All is set within a cylinder at the top of the door. Hence, it catches almost like a strike when closed. The advantage of this lockset is that there is no need for a bore hole. All that is required is a single dummy that is mounted on the surface. Understandably, many people prefer this first setting because it has fewer parts that can go wrong and is therefore rather easy to maintain, provided the right approach is used.
The second type is the spring loaded latch. This is also common in many homes but requires a passage function lever or knob. It can either be a residential grade or for commercial purposes and the size will reflect the level of workload that it is supposed to carry. Incidentally the inside knob is rarely used so one might say that it is rather redundant. In fact the keyed cylinder does not require a thumb to turn inside. A case in point is a storage closet. Here a specific setup is required. One of the adjustments that are done is the addition of a blank plate on the interior. The downside to such an installation is that it actually makes it very difficult to make an emergency exit.
The knob has never been merely decorative, although its size and shape are important. In fact it can have a lock within. This implies that it too has to be replaced when it succumbs to wear and tear. However, the basic set up will work in a variety of settings including cabinets and safes. Metal is quite tough and is preferred for business premises whereas wood is very good in aesthetic terms for certain residential properties. That is not to say that replacing a bolt requires the bolt to be replaced as well. One can start failing before the other. Nevertheless, it pays to check both parts on a fairly regular basis in order to ensure the functionality is as reliable as when first installed.