Re: Dragoons?
I think of them as mounted infantry rather than cavalry that can dismount.
In a defensive role they can be used as a rapid reserve force to plug gaps anywhere in a long line when they form, or counter flanking infantry.
Once your attacking foe is routed, mount them up and cut down the swine!
Attacking they can be deployed ahead of your army to control the middle ground and have freedom of deployment for your main line, but this is better suited to light infantry.
This is unless there is a section of high ground closer to the enemy than your own forces. Dismount on the slope facing away from the enemy to protect your horses from shot and cannonade.
More commonly, I use them as a flanking force to jab them just in the right spot behind their lines.
These is my favorite type of cavalry because of this multi-role capability.
"Either the wallpaper goes, or I do."
-Last words of Oscar Wilde