Lets face it, using almost anything but the knife blade on a SAK is a matter of compromise.(Even the knife blades aren't too special if you are used to a "real" knife) The scissors are sharp, but smalland relatively fiddly. The screwdrivers are OK up to the point where you find the screw is really well set or you're trying to put a screw into something good and hard (like oak). The saw is sharp but only 3" long at best, etc etc etc. The SAK is the ultimate compromise tool.
I EDC both a SAK and a Swisstool, and really feel lost without them. I love the things, and they have got me out of more fixes between them than I could list, but to be honest, even the Swisstool is only a compromise tool. Nothing works as well as the proper tool for the job. Try putting a dozen 3" screws in with the Swisstool and you'll soon hanker after a decent screwdriver. Try cutting firewood with the saw and you'll soon want a better saw. The list is as endless as the tasks you might tackle with the SAK or the Swisstool. The point is, who the hell wants to carry an entire tool-chest around with them 24/7 when they can usually get by with a good SAK ?
They are like the "Get Out Of Jail Free" card in Monopoly.... they might not guarantee that you'll win, but they sure help to keep in the game and it's damned handy to keep one "up your sleeve" for when you might need it !