Back when I was in college, our equitation coach was pretty adamant about making beginner/intermediate riders ride in plain flap, close-contact saddles all the time. I never really knew why, because I couldn't tell much of a difference the time or two I grabbed a saddle with rolls/blocks and padded knees.
Well, fast forward to a few months ago, and I started lessons at a new barn. All they had were the jumping type saddles with tons of rolls/blocks and padding. It felt absolutely bizarre. So, after a month of this, I went out and bought a used Crosby Prix des Nations, plain flap -- and it instantly felt like my former 'good ol' days' of riding.
It felt wonderful ... up until I did more than walk around in it. I was slipping and sliding all over the saddle, getting my legs too far forward, or having them slip back. I can say that after about 8 or 9 lessons in it, my leg HAS improved. I mean, it kind of has to.
It's still not as good as it could be of course, but enough that I feel more confident in it.
So, now my old trainer's preference made sense. And as my new trainer says: It'll definitely make you a better rider.