There is a lot of lunging going on prior to my clients mounting up because they want to let their horses stretch their legs. At this time of year, I think it's necessary to allow the horses to warm up in this manner so that their bodies can relax and move without someone immediately sitting on their cold backs. I have no concerns either way and whether I longe a horse before my ride depends on their age, level of training and my "thoughts for the day." I will often longe Wheels, even during the hot summer months, not to release energy or train...but to get him moving forward.
There is a very nice teenager in my barn who has a lovely thoroughbred. He is fairly hot and tight through the body. When she brings him in to longe, he's often very naughty, drags her around and gallops sideways for long amounts of time. For me, this is not effective and will eventually injure the horse, the girl, or someone else trying to work in the arena. It's also disruptive. Lunging should be a useful tool and not solely for "playtime." Other than Wheels, who I longe to get ramped up, not the other way around, I start horses right from the beginning that if they are in tack, they need to behave and go to work. If they are in a halter, they can leap, run, buck and have a good laugh. I try to differentiate between the 2 right from the start so they associate the surcingle/saddle with working and the halter with play. I talked with the girl about this theory and she got the idea.
She tacked her horse in saddle and bridle with side reins loosely attached. Right away, as I tried to send him out on the circle, he leapt in the air and tried to take off. I kept my ground and didn't let him go, simply reeled him back in like a fish and used a quiet voice, "steady." This happened 5 or 6 times before he understood this was not allowed. Finally, he moved out onto the circle in a tiny, mincing walk. I didn't want to encourage this, so I quickly went to trot. It too, was lacking in any form of swing and was very pony like in its movement. His hind prints were at least 2 hoof prints behind his front prints. He was very tight through his whole body, even his tail was poked straight behind him.
He'd get through a circle and take off. Again, I would begin to reel him in, speaking quietly, "steady," and when he would come back to trot, I'd immediately say, "good trot." I often will hear people telling their horse to trot repeatedly while they run around in circles. I've always believed that if the horse hears the work "trot" often enough, he'll associate it with the canter. You need to use the longe line and body language when you don't have the horse's attention.
By the end of the session, the horse was trotting, very forward, not completely relaxed, but much better. At least, the longing was effective and the horse learned something. The girl was able to repeat the exercise in the other direction and has a better understanding of what she should expect from her horse. With that said, hopefully she will be able to come in the arena and not have people groan when she arrives! Good luck!