[raynor]

In strategic combat, you can direct your fleet to capture the planet. Your ships will fire on the planet until the weapon platforms are destroyed and then land troops. But... if you have a large fleet, it is not uncommon to utterly destroy the planet by accident in the process. In tactical combat, you can control which weapons on your ships fire and stop firing on the planet precisely when the Last platform is destroyed so that you don't destroy any facilities.

With overwhelming odds, tactical vs. strategic won't make as much of a difference. But if the battle is fairly evenly matched, you will almost always be able to control your ship better than the AI. In particular, I recently founght a battle using fighters that had much different results in strategic vs. tactical. In strategic, my light carrier with 60 fighters was utterly destroyed by six enemy light cruisers equipped with Point Defense Cannons I. In tactical, I destroyed anywhere from half the enemy ship to all of them!