Locks, clips, studs, size, and speed.
As a teenager the thought of carrying a folder that didn't lock wasn't something I did.
Pocket clips and studs were important if I was going to carry a it, any folder with a sub 3" blade was not a primary folder at all, and I looked for knives I could flick open.
These things were so important to me that I cut an easy open notch and attached a pocket clip to my Buck 425 allowing me to spidy flick it.
Now I have no problem with a 2" bladed slipjoint in my pocket, I've realized I don't have to have a lock on a folder, and am no longer consider clips and speed an utmost requirement.