When talking fixed blades, unless its a special carry, most strong side sheaths, the knife is either drawn, and changed in grip, to get a solid saber, or to get edge out, or its drawn straight up, and its edge in reverse grip.
So, edge in becomes part of the equation, when including a factor of immediate need... you need it fast, no time to phck around changing grips, reverse grip edge in is probably going to be fastest I think.
With any knife, if you want it in reverse grip, you've got to flip it around, obviously... Now, flipping it from a saber grip, to a reverse grip, edge out, involves some dexterity, and has to be practiced to do effeciently... It involves tilting the knife up from the hand, placing thumb and middle-finger on each side of it, and spinning it, in the process this reverses the knife, it also turns the handle completely in the hand... this takes a lot of dexterity, and muscle control.
This is also how it would be done with drawing a folding knife, and then turning it into a reverse grip edge out, just have to get it open first.
In a fight, adrenaline pumping, there isnt a lot of that left. If you've trained for 3000 hours, just on this technique, maybe you can get it done without fumbling/slipping.
Now, pour oil, and salt water (blood&sweat) onto the handle and try it... *clatter* oopsie!

Now, turning it into reverse grip edge in, right after the draw... I draw my folder, by pinching the rear of the handle, between my thumb, and my index and middle fingers, and pulling out. Its an Emerson knife, with a Wave, (sorry if thats not cool to mention here, not trying to start a pissing contest, just sharing my thoughts) so its open when it comes out... and with my fingers like they are, already, its a simple move to let gravity carry the knife down into reverse grip... and this puts it with reverse grip edge in... once again.
And I find it easier to do than adjusting my hand into a solid saber grip, faster, and less dexterity needed.
So how I carry, I could draw fast, or once drawn get into a solid grip fast, with it in edge in.
Now, its only a split seconds diff in time... but how much diff is it in muscle movement, and dexteriy needed? A LOT.
I'm not a doctor, and I dont know how many muscles move for each, but just try it, see for yourself which feels like it takes more dexterity, and more muscle use to implement.
Now, saw your right hand was involved (holding a pistol), or hurt, and you had to reach around, and grab your right hand IWB fixed blade, with your left, its going to come out in reverse grip, edge out... again, knowing how to use it like that is important.
There are so many variables, so many...
Neither is better... they each have their attributes, and there is one thats the prefference for us all...
However, its equally important to train, and become good at, using the blade in a variety of grips, edge in, edge out, forward, reverse, saber grip, hammer grip, etc.
What about for the gunners? If forced to draw a knife, because its faster to get at than their concealed hand-gun, or needing the knife to hack at am arm/hand on a person trying to take their gun, they might be forced into grabbing the knife with a bass-ackwards grip... and even if they dont like Edge In, that might be how they get their hands on it... and thus should be familiar with its use. (this really goes for any of us, not just the gun ppl)
Knives for gunners... whats that you say? Guns are more powerful, guns are better right? But... but people should carry knives? DAMN STRAIGHT!!
And carry them in places you can access with either hand, gun hand, or weak hand... So you have a better chance of not having to get it from some bass ackwards position...
As I mentioned before, If someone has ahold of your gun/gun arm, how are you gonna make 'em let go? Well, one way is to cut the sh!t out of the arm holding yours.. with the knife in your weak hand.
Cant get to your gun fast enough? What about the folder or fixed blade?
Or even that ASP baton?
And who knows HOW you'll have to grab that weapon... the only opportunity you may have, might be in a bass ackwards grip to the norm, but if you can still put it to use, thats what counts!
yer trying to survive... not mince around with grip changes, and getting to the best weapon...
The best weapon is the one in your hand,, that you can use!
So even if you despise edge in grip... or any grip, I think its important to have an idea of how to use your weapon in that grip...
Even if Edge In doesnt work good for you... its prolly smart to get familiar with it... just incase... cuz, incase ya hadnt noticed, sh*t happens... and its rarely predictable.
Be a defensive boy scout, be prepared.
As is commonly said around these parts, you're fighting to live... there is no one perfect weapon... and no one worst weapon... no one worst grip... no one perfect grip...
Its dictated by the need at the time. Bass Ackwards, but knowing what to do with it, is definatly the upper hand to nothing at all. Situational Demands are that you live, and to do that, you gotta make the best use of whatever weapon you get your hands on (be the Bad Man with it...)
Sorry if this is a rehashing of things already said... just had a few more thoughts, that i wanted to add, so excuse it if un-original beyond belief material.