Sometimes we need an external pair of eyes. When youy attend, go with your magazines full and your ego empty.
We will all reach a certain "performance plateau" when we train on our own. We cannot see where we are making mistakes. We can see the results, but not the how or why we are making them. Or, we have to acquire new skills to get us moving again.
In many aspects of our lives, we must occasionally consult with an external source of knowledge. Someone who can see all of us and knows what to look for. A firearms instructor who offers private lessons is one of those people. He (or she) can see what you're doing, both the good things and the bad things. From that point, it's their job to reinforce your good habits, help you to replace the bad habits with new good habits and teach you new skills so you can start moving up the mountain again towards the next plateau. The private lessons are for external feedback to providing the minor adjustments to get us past a stuck point.
There are also group classes. I personally would love to get to stay at Thunder Ranch in Oregon, or the Warrior Poet Society facilities in Dalton, GA for a month and take class after class on every type of weapon I have. That being said, that would be a bad idea and let me tell you why.
First of all, After a weekend (or week) of intense training and learning of new skills, a person must take the time to properly grok what they have learned and practice them enough to make those skills an integral part of themselves before you go back out and learn even more skills. As with all training, absorb it, then practice it. Once you are happy with your skill level from that training, then I would happily wave at you as you head out to the next training. Depending on how fast you absorb and master new skills (and your bank account refills) I recommend no more than 2-3 classes a year. Unless you have the time and budget for 200-300 wounds a week, I would lean to 1-2 times a year.
A fantastic point from the Armed Attorneys on YouTube: Don't frame your certificates from such places on your walls, or post them on Social Media. This, like I said in Blinging your Blaster, it will be used against you in court.