I've been wondering what would happen if someone only did the big three.

If you got a healthy person that had never worked out before, showed him how to squat, bench and dead lift properly. And he only did those work outs.

Would he continue to progress? Would he end up getting hurt?

He would progress for awhile, and eventually reach a limit that would require him to add in assistance work to further progress. That limit would be different for everyone. He would likely stall on bench earlier than the other 2 lifts. He would obviously develop muscular imbalances, but not necessarily suffer an injury.

His shoulders would most likely get pretty jacked up as well.

The trainee would be fine, although the trainee would have to do some prehab work

I have trained with 95% of my training sq/bp/dl. I have progress to a 305+kg squat, 227.5kg bench, and 272.5kg deadlift at 93kg single ply (currently down to 86kg and just as strong). I think that I agreee with detazatoth that the 5% of prehab work (and some upper back) really helps me but frankly I found that spending much more time on it didn't work for me personally.

There are a million ways to train and progress and training purely (or at least close to it) the big 3 is a viable option that can work very well. Perhaps not for everyone, but certainly should not be disregarded as causing injuries and having a distinct ceiling that cannot be passed without assistance work.

Don't know about the big 3, but tons of people have success with the big 4. Sorry for the kind of irrelevant answer.

Are you saying you have a 500lbs bench from doing 95% of all your pressing volume from nothing but Bench Press with very little if any assistance...?

just add in rows and you're set

For a two or three year period......probally few problems.
For a decade......??????

squat, bench, deadlift, chin up, row.

If I really had to choose the minimum amount.

Mike Tuscherer believes in very little assistance work if any, he explained that for him assistance made him very good at the assistance movement, he cites having a 500lb GM...but he had the most carryover from doing the big three in different forms. Im slowly breaking out of being an assistance movement junkie and following his programming based almost solely training the big three with very little assistance work

Of course he would progress. But shoulder injuries might occur since you would be benching and not doing any pulling. So adding in something to work the post delt and doing shoulder mobility would be necessary.

I posted a link to Korte's 3x3 but for some reason the post is gone. That said, it's an example of a program that only uses those three movements.

yeah you're shoulders will be pretty pissed off, also among other things most people need direct tricep work to keep their bench progressing

Check out Doug Hepburn

I only did the big three for about a year and I had to stop due to injury. My anterior core became too weak compared to my posterior muscles, which affected my hips, and my shoulders began hurting a lot also. I'm sure some individuals could do this, but I couldn't handle it.