in his opinion more important than what was carried was that you always carried in the same manner and actually practiced drawing. His point was that in a pinch you needed the draw to be instinctive, once the decision to draw had been reached. The moments needed to remember where you were carrying your firearm that particular day could be critical.
I've tried to practice this but frankly the best I've been able to accomplish is two locations. One location is a right hand IWB and one a left hand pocket carry, depending on what cloths I'm wearing and firearms I'm carrying.
So what about you? Do you standardize or switch around.
Let me say your friend's dad was correct. I will carry it past that. Always carry the SAME gun.
Doing the same thing, each time, in the same way is what made the Ford assembly line a success. If you carry one way one day and another the next, you will not be able to react as promptly as you should if the SHTF.
Even more important, and many ignore this for some reason, is carry the same gun. Different guns work in somewhat different ways. Maybe is it something as simple as a different safety, a SA vs DA, a short slide vs a long slide or such. People tend to know a gun works more than how to work the gun. When you carry different guns, each will act and fire differently.
Back in the 60's, the Army furnished me a 1911. I had to know that gun inside and out. They taught me to take the gun apart and reassemble it while blindfolded, they taught me how to use it single hand, weak hand, laying down, standing up and they let me learn how the gun fired. I knew where the bullet would hit when I fired it.
Yes, holster is important but it is the gun that will save your hide.
For me, I used to practice often in this manner but as I aged, I slowed down some. I would drive down the road listening to the radio. Each day I would pick a buzz word, maybe it was the day of the week or the month. When that word was said on the radio, I would draw my gun. I got pretty good at doing it inside the car. At home, I did the same with the tv set. Each time I went for the same holster and the same gun. I could do it in the dark and do it in bright sun, the same way each time.