The fluid inside the blister is the body's very own medication, and should be kept where it is needed, at the site of the damage ie blister. If you burst it even though you have cleansed the skin you have still made an opening even a small one where germs, which are much smaller than a needle point, can get in. A common place for blisters is the heel and by simply applying a dressing, any friction to the skin which is what made it in the first place, is alleviated. The technique shown to you by your dad but you have never seen since is quite simply not the correct treatment for blisters, it's that simple, he may well have shown you his way of dealing with them, but if it involves bursting them or piercing them then it is not the correct treatment for them I can assure you. Many things have been taught in days gone by for example treating a burn by putting butter on it, but that is probably about the worst thing you can do, but for many years a helluva lot of folks thought this was the correct way cos their mother or granny had taught them this. Ask any doctor, medic, or check in any first aid manual for the correct way to deal with blisters, you will see I am correct, regardless of what you have been shown in the past and by whom, and I mean no disrespect to your dad or anyone else. Has your proper training, as you put it, ever shown you to treat a blister by puncturing it, no by your own admission, so please accept that what I am saying is right, I can assure you it is absolutely correct and valid.