I for one have never done it.
However, I'm beginning to think it may be a useful tool for my 2-yr-old, who I just started riding.
So far, he hasn't been the brightest crayon in the box but he is doing okay. I've ridden him 5 times. The future NFR-qualifier just had his first ride!! I keep my "rides" pretty short around 10 to 15 minutes. He's still just a "baby" so we're just taking it nice and easy. I mostly just like him having the exposure at a young age, because I feel its easier when I bring them back at age 3, after being a horse for the winter.
I always start my colts in this order (when it comes to the bridle):
1) Put the bridle on (no reins) for about 10 minutes on several occasions, so they can get used to it in their mouth.
2) Start asking to give to the bit in both directions, using the halter as reinforcement.
3) Start asking to back up in the bit, using the halter as reinforcement.
4) When he's giving in all directions after many sessions, THEN I get on.
And I always go through this little "flight check" before I get on him, to make sure he's paying attention before I get on.
He does pretty good about giving to the bit most of the time. Every once in a while, though, his nose goes in the air and he resists. I keep on him until he "gives" properly so he's not getting away with it.
Now I figure that he'll continue to get better with time, but I also wonder if tying the reins around will help him figure it out sooner, rather than later?
I've never done it, so I guess just looking for opinions on it either way.