Yes, it knocked Italy out of the war, but it didn't seem like Italy was contributing all that much to the Axis war effort, anyway. And the whole venture didn't satisfy Stalin's demand that the Allies open up a second front in the West (didn't he label it as a "sideshow?" It seems like to me that a lot of Allied troops and Italian civilians (not to mention surrendered Italian military personnel who were then murdered by their former German colleagues) died for very little benefit. I don't want to venture too far into the counterfactual, but perhaps all of those resources could have been better used by landing on the Mediterranean coast of France.
Italy was originally chosen by the Allies (Britain in particular. The Americans never really wanted to invade) as it was a perfect jumping off point from Tunisia in North Africa to Sicily and then upwards through the Mezzogiorno to Rome. France was also known to be much more heavily defended with construction already underway on the Atlantic wall and other formidable coastal defenses.
It seemed like a good idea but poor coordination and planning, stalwart German defense and the harsh mountainous Italian countryside turned the Italian campaign into a blood bath often likened to the carnage of the First World War.
It did help in that Germany's manpower was stretched even further to breaking point. They were already fighting savagely after Stalingrad and Italy's surrender meant that there was no more Italian support on the Eastern Front and that Mussolini, a key leader in the Axis was removed.
Churchill dubbed Italy "the soft underbelly" of the Axis but after battles like Monte Casino among others, it got the much more apt title, "Tough old gut."