If I am carrying on actual working knife for my job, I always want more than one blade. Why? So if I damage the edge, the knife isn't worthless until a resharpen. I carried a large CASE stockman for years as a primary knife and it did all you could want a knife to do. It sharpened my pencils (when I was a house framer), cut banding straps, trimmed molding, cut sandwiches, stripped wire, and on an on. The CASE (although not the workman series) was up the job in spades. After getting some money together, I alternated it with a large CASE copperhead with a clip and spear blade.
I was finishing up a remodel I am working on last week and found some paint drips on a wall. I cut them flush as I always do, then slap a bit of paint over the place where the drip was, and off I go. When touching up a door frame, I pulled out my medium stockman to slice off a drip from a previous paint job, and couldn't cut if off. I worked on the drip, and finally heard an awful scraping noise. The "drip" was a small trim staple that hadn't been sunk when the door frame was made and had been painted several times. Needless to say, the stapled ruined the edge in the blade.
But... with two others left, I was still able to finish up the trim that day (sheepsfoot is my favorite for trim work) without any problem. Didn't miss a beat.
That being said, if I was opening mail, cutting some packing tape on occasion and cutting up an apple for lunch, I would probably be fine with any single bladed knife.
Part of my problem is that as a cutting tool, I don't like to use a knife when it is starting to get dull. So a fresh edge is a good thing for me.
Robert