I used to prefer a serrated edge on the ship, as it seemed to work better on larger lines and that was usually what I was cutting. Plus, incidental contact with metal surfaces was common; sooner or later, even the plain edge knives were serrated.
In retrospect, a plain edge could've done just as well, had I known how to sharpen one properly back then.
There is one time that I was extremely happy to have had a fully serrated edge and it's a bit of a story so please, bear with me here. (If you're not in the mood to hear it, by all means move on - I tend to ramble a bit.) Here goes:
A while back, I was in search of a large, fully serrated, Americanized-tanto style folder. This, to me (at the time), was the perfect format...nearly indestructable, durable edge, and a secondary edge that would make for a good chisel/scraper should the need arise. Not too many people make these I guess. I did eventually find one and got the biggest one available - a 5". Good thing, too.
One fateful Friday I was tasked with heading to base first thing in the morning for PT, then heading out to my primary place of employment - a naval reservation in the middle of nowhere, 15-20 minutes from the base. As I was departing from the base, I noticed an odd vibration toward the rear of my car. As it was old and had been rode hard and put away wet more than a few times during its interesting life, I was not surprised and was mentally preparing myself for a Saturday of wrenching.
Several miles out the gate and on the highway, my right rear tire delaminated. Ever seen those "razorbacks" left on the shoulders by the big rigs? That's what happened to me, although not quite so badly; the detached strip of rubber remained anchored at one end.
Although it was still on, it was striking my car so hard that the mud guard detached in only a few seconds and the wheel well was taking a beating. I made it to the shoulder but I could not continue driving like this. I did not have roadside assistance and did not care to pay for a tow. The Kitsap Mall (which had a Sears, complete with tire shop) was only a few miles away. My spare had dry rotted and was useless. It was time to get creative.
I was lucky. The knife was clipped to my uniform, which was laying in my back seat. I figured that if I could cut off the offending strip, I'd have have a dangerously thin tire but it would hold long enough to get me to Sears. (Even if it was flat, I could probably make it.) I got to it. Part of the way in, I realized that the detached strip contained the belt and I'd have to saw through that as well. It took about ten minutes to get all the way through; the blade was too hot to touch when I was done.
Long story short, I made it to Sears and the folks there got big kick out of the whole story. (Not that it saved me any money.) I don't believe that this would've been possible with a plain edge. It didn't save lives or anything, but it saved me a good chunk of change.
As a final note, I recently found this same knife sitting around gathering dust; its serrations were damaged beyond usefulness. I took it to the belt sander and made it a plain edge. It's now back in service.
Lessons learned? I've only ever needed a serrated edge once, but when I needed it, I
needed it. That being said, put me in the plain edge camp. I see a pattern here with myself included - starting with serrations and ending with plain edges. I personally don't care for combination edges; in my mind, they're a compromise that combines the worst of both designs unless the blade length is long enough to rule out folders.
Now that I think about it, a politically-correct multitool usually features a plain edge, a saw, and possibly a combination edge as well - the best of both worlds. I never seem to use mine for anything other than a pair of pliars, though.
Sorry for the ramble but this is one of the stories that I trot out for folks I know who don't see the need for carrying a good knife. I left the manufacturer's name out intentionally as this isn't a discussion of brands, but of designs.