Whoa, kuggur.

Whoa indeed Masia
May have come down somewhat heavy, but I am interested for what kind of scenario people think they need a knife for actual fighting in their daily life. Who knows, it´s an international forum, maybe they live in a Mexican slum or something.....

I have been threated with knives 2 times; during the first my opponent was another Italian with different political views than mines, and the 2nd time my opponent was a Moroccan guy. They both were drunk.
During another brawl my opponent had a brench; luckily I've never been wounded by these weapons but I once saw a stabbed guy and I can tell you the blood ran like rain, and it is not a nice thing to see.
I also saw beer bottles being used as blowing/throwing weapons, and these are quite effective, too.
Not to mention cobblestones, but I'm running OT now.
Peace 
Mauro.

A knife could be a useful LAST RESORT defense weapon.  I prefer a good, stout walking stick.  It has reach plus it's possible to render your opponent helpless without killing him.  A few years ago I was attacked by a prowler and used a small (like for little kids)  aluminum bat to defend myself with.  You woudn't believe the legal mess.  This was a prowler, on my property, that started the incident by attacking me.  I guess the law wanted me to let him kill me or my daughter.  I can only imagine the mess I would have been in had I used a knife.  I'd probably be in prison right now.  If you ever use a knife to defend yourself make SURE that you are 100%  covered, like with many friendly witnesses and no other possible option.  Even this won't be enough to save you from being arrested and a lengthy, expensive, mentally draining, life disrupting court proceeding. 
   BTW, the prowler killed himself prior to this going to court so everything was dropped.  Nice story... the moral... the law frowns on you using any weapon to defend yourself, apparently regardless of the situation.

"if one of is to be tried, and one to be buried, I will be the one that is tried" ~ El Fego Baca

It really depends on how you approach self defense and fighting. Waving a knife around is (in my opinion) a horrible way to de-escalate a situation, but in a self defense situation killing the other person is very much on the table. Not over money. Not over pride. Not if running the hell away is a possibility. But if there is no option but self defense, using a knife (as opposed to brandishing a knife) may well save you or a loved one's life. There's an important difference between wearing a weapon and carrying a tool/weapon to use in an appropriate situation.

As an aside, a stout stick or a baseball bat can also easily kill a man. the difference between knocking someone out and killing them is not as clear cut as TV would have you believe. The human body is both more resilient and more fragile than we often realize.

A dull knife is terrible for fighting(I call it fighting but reallly mean SD, not like dueling in regular life). So I, and most that study knife fighting carry one that isn't really for utility use just for those really bad occasions. Most Fri and Sat are usually at home   often with my best friend, saturday was pretty much spent raking leaves, making self bows, and slinging. That's pretty typical for the days I don't spend partying.  

(jk for those without a sence of humor)

Thank God I have never had the occasion to have to use my SD knife, but if the need arises the saying "better to be judged by 6 than carried by 12" comes to mind.

I have been studying knife fighting for 4 years and Kenpo for 8 years and thankfully have never had the occasion have to use them (I am pretty good a cooling down a controversy, if I need to)

You can use a knife nonlethaly btw, if you read the armed citezen in The Rifleman (NRA magazine) you probably know that most gunshot victims no longer feel like commiting crimes with a hole in them and run away and are ususally picked up by the nearest hospital.  
As for using one for self defence I really wouldn't use it unless I really had to, I can use just my hands pretty well unless there were just too many or they had guns in which case the knife would be a force multiplier. 90% of the casses (99% involving common thugs) where a knife is pulled by the defendant the other guy runs away. Thugs look for victims, not guys yelling at them with a fighting knife. I read an account on Cold Steel forums of a guy who pretty much had just that happen too them he had 5 or so (pridefull) guys come up to him and his wife wanting to fight (him) he pulled his knife out (not planning on fighting) and well, they no longer felt the need to fight.

My fighting knife is for last resort, as I can probably do what I need to with my hands, but it's nice to have a last resort.

We haven't had a good thread on knife fighting for a while, this should be fun.

Last thing, here is a great soruce for an over view of SD knife fighting. This along with practice will really increase you chances of surrvivasl in really bad odds. (watch video) http://www.coldsteel.com/warriorsedge.html  parents got me this a few Christmases ago, best dvd out threre on knife SD.

back to the original question.....

I carry a gerber multi tool 600, though almost never use the blade.

But my main edc knife for the last 18 months has been my mantis buzzard.
Just the best engineered and made tool I think I've ever owned - even better made than the gerber.