Gunsmithing kits usually come with a large number or slotted driver bits. This is because there are many sizes of slotted screws in firearms, and it is important to use one that properly fits to avoid damaging the screw - especially on antique firearms, where a replacement screw may not be available, and the damage can effect the value of the weapon.
For a more day-to-day example, go look at a wall switch, network drop, or electrical outlet cover. Often, these use slotted screws for aesthetic reasons, and they are quite easily damaged. Once you spot a damaged one, you can't help but notice it every single time. Well, *I* can't. Then again I line up all the screws vertically to make it look better, and so I can tell if someone else has taken that plate off.
Klein keystone and cabinet screwdrivers are designed to fit American fasteners in electrical applications, which is why some people complain that they don't fit well on other screws. They are specified to that particular purpose. Same with Snap-On for automotive purposes. There is a tiny difference, but it is important.
Old WF Craftsman slotted screwdrivers didn't fit their intended screws very well. Example: A 1/4" was really closer to 9/32" and would destroy a wall plate screw. I've had to grind them down with a file and sanding block to get them to properly fit. Regular weekend warriors would often use these for prying, chiseling, punching, stirring, poking, digging, scraping and all kinds of things except turning a screw, so I suppose it didn't matter much to them. But a high quality set of hollow ground drivers or bits can make all the difference when it really counts.
