Actually by this period there was not all that much difference (in the British service) between light and heavy cavalry, not in horseflesh or men. The difference came, like you say in deployment, however even then this was more traditional than practical, each grade of cavalry was required to skirmish as outposts and charge with cold steel.

The objective of cavalry warfare in this period was always rally and reform after a charge. Even heavy cavalry if controlled properly should be able to continually engage the enemy until forced to withdraw, which it will strive to do in complete order so as to be available to charge again.

The mounted service was actually one of the most demanding in a general action, because of the niceties involved in trying to keep your men formed and ready. For example ideally cavalry of any grade would move forwards with at least one reserve, at best two. Cavalry officers would know that when the lead squadron in engaged an enemy, even if it is victorious, is effectively broken until it has reformed. Pursuit should ideally be taken up by the succeeding squadrons and so on. Reserves were essential because the enemy also should be expected to deploy tiers of cavalry reserves for the same reason.

The difficulty in rallying squadrons that have successfully broken the enemy and keeping a strong reserve was something the French were rather good at, but only a few British Generals maneged to impliment it.
While horses tiring was an issue, it all depended on the circumstances in which, and how you used them that dictated wether blown mounts was an issue.

Josh.