Misleading thread title actually since they are not mutually exclusive nor is one a superior method over the other... ideally you want both.
Soo training... The good.... it gives you all the rudimentary skills you need with the least expenditure of rounds fired. It also can... but not always... teach you things you would never learn on your own.
The bad.... it is often very specific. For one type of shooting or firearm. The skills learned will rarely transfer seamlessly to other styles of shooting or firearms although the basics never go out of style.
Sooo... just shooting. Worst case scenario... you buy a gun and are completely on your own. You learn each thing about the art of shooting by simply shooting thousands and thousands of rounds. Some people are 'naturals' but by no means most. Most of us learn by having someone who... is a good shooter or maybe no better than most... show them the rudimentary stuff. Trigger.... grip.... sight picture....even stance... all these things can be learned by shooting countless thousands of rounds. Expensive... but fun for some. I learned to hip shoot by shooting thousands of rounds at small objects at short/medium range. There really was no 'training' for such a thing. Grip... bloody hands or black eyes can teach you that. Sight picture.... again... thousands of rounds combined with trigger control. Stance... breathing.... this is where training can save years.
Ok... one thing people will say is that bad habits are just re enforced by doing the same thing over and over. On the surface this is correct. And is wise advice for most people. How many rounds does the average shooter shoot a year? Some people I take shooting I take em like 5 times a year.... they have jobs whatever... they may shoot 100 or 200 rounds a session.... that is a thousand rounds a year or less? I used to shoot more than that a week (no more) All my bad habits.... those that made me less accurate say.... melted away after 20-50k rounds... LOL... What I learned was.... when I did good... I tried to do that again. A bowling pin shooter I knew who was famous at the time.... saw me shoot at pins. Three were perfect... three more shots were not. He simply said...."do what you did on the first three"
Sooo shooting a lot... we all have good days and bad days. On a bad day? honestly? I have no clue what is going wrong... or.. .very little clue. On a good day... I can tell when the gun goes off if it was a good shot or not.